THE DISAPPEARING FLOOR

Once again Frank and Joe Hardy accept the challenge of a puzzling case when their famous detective father asks the boys to assist him in tracking down a notorious jewel thief and his accomplices. The trail leads to the outskirts of the Hardysâ€™ home town and to a weirdly guarded mansion on the old Perth estate.

With their chubby, ever-hungry friend Chet Morton, Frank and Joe tackle another mysteryâ€”one which has baffled the town of Bayport for many years: What caused the sudden death of Old Man Perthâ€™s nephew who inherited the mansion when his uncle died?

A disappearing floor, a huge, savage-looking hound, a galloping ghost, a college professorâ€™s startling invention are just a few of the strange elements that complicate the boysâ€™ efforts to solve both mysteries.

Before Frank and Joe finally discover the mysterious circumstances under which Perthâ€™s nephew died and also bring the jewel thieves to justice, the young detectives need all their sleuthing instincts to extricate themselves from one of the most harrowing situations they have ever faced.

âFrank! The room has no floor!â

Copyright Â© 1992, 1964, 1940 by Simon & Schuster, Inc. All rights reserved.

Published by Grosset & Dunlap, Inc., a member of The Putnam & Grosset
Group, New York. Published simultaneously in Canada. S.A.
THE HARDY BOYSÂ® is a registered trademark of Simon & Schuster, Inc.
GROSSET & DUNLAP is a trademark of Grosset & Dunlap, Inc.

eISBN : 978-1-101-07633-0

2008 Printing

http://us.penguingroup.com

CHAPTER I

Weird Screams

âHEY, Frank! Isnât that the black car Dad told us to watch for?â exclaimed Joe Hardy.

A sleek foreign sports car with a dented trunk had just whizzed past the Hardy boysâ convertible as they drove through the downtown section of Bayport.

âSure looks like it!â Frank speeded up in pursuit.

Dark-haired Frank Hardy, eighteen, and his blond brother Joe, a year younger, had been cruising the streets on an errand for their detective father. The August evening was warm, and the boys had put down the top of their convertible.

A few blocks farther, the sports car stopped for a red light. The Hardys pulled up behind the trim vehicle. In the glow of a nearby street light they were able to scrutinize the automobile more closely.

âThat must be the right car,â Frank muttered. âItâs not likely there would be two of the same model in Bayport with dented trunks.â

The lone occupant of the sports car was the man at the wheel. He wore a dark hat. Frank and Joe could see only the back of his head.

âDid Dad give you any details on the case when he phoned?â Joe asked, as the sports car spurted forward on the green signal.

Frank toed the accelerator and shook his head. âNo, he didnât have timeâit was just a hurried call from New York.â Mr. Hardy had said that before leaving Bayport he had spotted a car like the one the boys had just seen. He thought he had recognized the driver as a notorious jewel thief named Noel Strang, and had told his sons to look up the criminalâs photograph in Mr. Hardyâs private criminal file.

The boysâ father formerly was an ace detective in the New York Police Department. He had moved to the town of Bayport to open his own agency and soon had become known as the ablest private investigator in the country. Frank and Joe had inherited Fenton Hardyâs detective abilities and often helped him on his cases.

The boys drove on, staying behind the sports car which now sped into a residential area. The streets here were less well lighted, but the boys were able to keep their quarry in view without tailing it too closely.

âLooks as though heâs heading out of town,â Joe remarked.

âDid you get the license number?â

âYes. I jotted it down at the traffic light.â

In a few moments the black sports car shot out of the Bayport area. Soon it disappeared from view around a bend in the road. Frank switched off his headlights, hoping to make the convertible less noticeable. But the driver of the other car seemed wary of pursuit. As the convertible rounded the bend, its driver increased his speed. The distance between the cars was widening.

âHe must have spotted us!â Joe said.

âHeâs sure opening her up,â Frank agreed. âThat baby looks powerful! Good thing we tuned up this engine last week.â

The convertibleâs speedometer needle rose as Frank gunned the engine. Slowly the gap began to close. They were approaching another bend in the road. Suddenly the sports carâs exhaust belched out a thick purplish mass.

âItâs a smoke screen!â Joe cried out. âHeâs using a fogger attached to the exhaust pipe!â A split second later the boysâ eyes began to smart and water.

âGood night!â Frank exclaimed.

Hastily he switched on their headlights again, but the beams could not pierce the thick pall of acrid smoke that enveloped the road. The convertible was almost at the sharp bend!

Frank slammed on the brakes. Half blinded, he could only guess at the location of the white line. He spun the steering wheel and the car slewed wildly across the pavement. With a jarring thud it finally came to rest on the far shoulder of the road.

âJumpinâ jiminy!â Joe sat quivering with shock, trying to steady his nerves.

Frank, also shaken, drew a long breath. âGood thing there was no car coming the other way or weâd be junk by now!â

âCan we risk getting back on the road?â

âWeâd better not,â Frank decided. âI canât see a foot away from us. If thereâs any traffic coming, weâd be asking for a crash.â

Joe agreed and added, âLetâs make sure weâre clear of the pavement.â

Clutching handkerchiefs over their noses and their tear-streaming eyes, the boys climbed out. In the smoke and darkness, it was impossible to determine their exact position, but Frank checked with his foot and found that they were well off the pavement. The convertible had landed against a hillside bordering the road.

Frank and Joe chafed at the delay, but there was nothing to do except wait for the smoke to clear. Meanwhile, they clambered up the hillside, coughing and choking, to reach clear air.

âDid you notice the smokeâs color?â Joe gasped. âThat was no ordinary smoke screen!â

âItâs a smoke screen!â Joe cried out

âRight. Sort of a combination of smoke and tear gas.â

After a few minutes the murk had dissipated enough for the boys to return to their car and swing back onto the road.

âNot much chance of finding that man now,â Joe said glumly.

âLetâs keep our eyes open, anyhow. There are houses along here and a few turnoffs. We might spot the car parked somewhere.â

The Hardys followed the road for several miles but did not see the sports car. Disappointed that they had lost their quarry, Frank and Joe turned around and headed for Bayport.

Halfway back to town, they saw a flashlight being waved frantically from the roadside. âWonder if thereâs been an accident,â Frank said.

âI donât see any car,â Joe replied. âMust be a hitchhiker.â

Frank slowed to check. The person who was signaling immediately jumped into the glare of their headlights. He was a chunky, round-faced youth about their own age.

âChet Morton!â Joe exclaimed in surprise.

The stout boy looked excited as he flagged them down. Frank braked to a halt and Joe flung open the car door. âWhatâs wrong, Chet?â

âJoe! Frank! Boy, what a lucky break you two happened along!â Chet was puffing and trembling and looked pale. He was wearing hiking shorts and had a knapsack slung over his shoulders.

âJust see a ghost?â Frank asked as their friend climbed into the back seat.

âI d-d-didnât see a ghostâbut I sure heard one! âChet replied.

Frank and Joe exchanged puzzled looks. âWhat do you mean, you âheardâ a ghost?â Frank asked.

âJust what I said. It screamed at me.â Chet shuddered. âO-oh, it was horrible!â

âAre you kidding?â Joe put in.

âDo I look as if Iâm kidding?â

âNo,â Frank said. âYou look as if youâd been scared out of your wits. How about telling us the whole story?â

Chet explained that he had been on a rock-collecting hike. Late in the afternoon he had stopped to eat a picnic snack and then had dozed off.

âSnack my eye!â Joe chuckled. âYou probably stuffed yourself so full you couldnât move, and dreamed about this ghost.â

âAll right, all right,â Chet retorted indignantly. âSo I like to eat. Do you want to hear my story or donât you?â

âGo ahead,â Frank urged.

âWell, I slept longer than I expected to,â Chet went on. âWhen I woke up, it was dark. I was somewhere over in the hills west of here. I had trouble finding my flashlight. Then I saw a funny-looking tiled surface.â

âTiled surface?â Joe repeated. âWhat do you mean by that?â

Chet shrugged. âI donât know what else to call it. It was flatâlike a floor, about ten feet squareâand inlaid with little colored tiles. But the funny thing is, there was nothing else around except trees and shrubs.â

The colored tiles, Chet added, formed a curious design resembling a dragon.

âI went over to get a closer look at it,â Chet continued, âand wow! Out of nowhere came a horrible bloodcurdling shriek!â

âSo you scrammed, I suppose,â Frank said, grinning.

âYou bet I did! The voice shrieked after me, but I didnât catch what it said.â Chetâs eyes bulged with fright at the recollection. âI kept running till I hit a dirt lane, and followed that out to this road. I was hiking home, then you guys came along.â

âHow about taking us back there?â Joe said.

âYou think Iâm nuts? Honest, if that wasnât a spook, it must have been some bloodthirsty lunatic!â

âOh, come on!â Frank urged. âMaybe it was just someone playing a trick on you. Letâs find out.â

Chet was unwilling, but finally gave in. He directed Frank to a dirt lane turnoff which the Hardys had passed about fifty yards back. Frank drove slowly along the lane until Chet said, âRight here! I remember that big oak tree!â

Frank stopped the convertible. The boys took flashlights and climbed out. They went up a slope which gradually flattened. The area was wooded with hemlock and cypress trees, and the ground between them was overgrown with weeds and brush.

âThereâs Chefs trail,â Joe said, shining his flashlight on some trampled grass. âIt leads over that wââ

A hideous scream split the darkness! Then came a weaker scream, followed by a hoarse, croaking voice. âTh-th-the floor!â It sounded like the gasp of a dying man!

Chet froze in terror, but Frank and Joe immediately ran toward the sound, playing their beams back and forth amid the undergrowth.

âOver here, Joe!â Frank exclaimed suddenly.

Joe ran to his brotherâs side and saw a man lying face down on the ground. Frank turned him over gently. The man was big and balding, with thin, sandy-colored hair. His face looked deathly pale. Frank tried his pulse as Chet came lumbering up.

âIs he d-d-dead?â Chet stammered.

âNo, but his pulse is weak,â Frank murmured. âHis skin feels clammy, too. Looks as if heâs suffering from shock.â

The Hardys could detect no signs of injury or broken bones.

âWhatâll we do with him?â Joe asked his brother.

âBetter get him to a hospital.â

The boys carried the limp figure to their car and laid him on the back seat. Chet sat up front with the Hardys. Frank swung the convertible around and sped toward Bayport.

As they reached a wooded area on the outskirts of town, their passenger revived and sat up. âPleaseâstop the car!â he begged weakly.

Frank pulled over. âWe were taking you to the hospital,â he explained.

âYou were unconscious,â Joe added. âWhat happened?â

âIâllâIâll tell you in a moment,â the man said. âRight now I feel woozy. I think the motion of the car was making me sick. Would you mind if I get out and walk up and down a bit?â

âNoâgo ahead,â Joe said sympathetically.

Chet leaned back and opened the door. As soon as the manâs feet touched the ground, he slammed the door. His face contorted into an ugly expression.

âIf you boys know whatâs good for you, youâll keep your mouths shut about this!â he snarled. âAnd Iâm warning youâdonât try to follow me!â

He darted off into the darkness of the surrounding trees!

CHAPTER II

Telephone Tip

THE three boys were stunned by the manâs unexpected threat and actions.

âOf all the creeps!â Chet spluttered when he found his voice. âHowâs that for gratitude?â

âIâm going after that guy!â Joe exploded. He yanked open the door and started to jump out, but Frank stopped him.

âHold it, Joe! Youâll never catch him now. Besides, he may be armed.â

Joe realized the wisdom of his brotherâs advice and reluctantly climbed back into the car. The neighborhood was run down. It was poorly lighted and had numerous vacant lots and small factory buildings. The stranger already was out of sight and doubtless could find plenty of hiding places if pursued.

âIâd sure like to know what that fellow was afraid of,â Joe muttered as they drove off. âAlso, how he came to be lying back there, unconscious.â

âSo would I,â Frank said. âWeâd better notify the police.â

âLook, fellows, IâuhâIâm pretty tired,â Chet said uneasily. âCould you drop me off home first?â

âWhatâs the matter?â Joe teased. âAfraid the police may hold you as a suspect?â

âI told you Iâm bushed!â Chet retorted. âBesides, you Hardys are always getting mixed up with crooks and mysteries. That kind of stuff makes me nervous!â

Frank and Joe grinned in the darkness. It was true that they had worked on a number of exciting cases since their first one, The Tower Treasure. On their most recent adventure they had solved the mystery of The Twisted Claw.

After dropping Chet off at the Morton farm, the Hardys drove to Bayport Police Headquarters. Here they found Chief Collig working late. The husky man smiled broadly as they walked into his office.

âYou boys busy on another case?â

âWeâre helping Dad,â Frank explained. âBut something else came up.â He told about the unconscious man who had later revived in their car and fled after threatening them.

Collig agreed that while the episode was strange, apparently no crime had been committed. He telephoned the fugitiveâs description to the police radio dispatcher to be flashed to all prowl cars, with orders that the man be picked up for questioning.

Frank told him about the boysâ pursuit of the black sports car and the smoke grenade that had forced them off the road.

âNoel Strang, eh?â The chief frowned. âIâve heard about him. Slick operator, but heâs not on the âWantedâ list right now. Do you know why your father is after him?â

âNo, we donât,â Frank said. âDad just asked us to trail him and try to get a line on what heâs up to.â

âWe got the license number,â Joe added. âBut weâd like to know if the man we were following was Strang. We didnât get a good look at him.â

Collig jotted down the number. âIâll check it with the Motor Vehicle Bureau. I appreciate your stopping by.â

The boys went outside to their convertible. As Frank felt in his pocket for the car keys, his expression changed to one of annoyance. âIâve lost my pocketknife, Joe. Wonder if it dropped out back there when I was bending over that fellow?â

âCould be,â Joe said. âWe can search for it tomorrow. I want to take a look at that tiled square Chet told us about.â

âSame here!â

Frank took the wheel and drove off through the late-evening traffic. Suddenly a red light flashed on their dashboard short-wave radio. Joe picked up the microphone.

âJoe Hardy here.â

âGood evening, son.â Fenton Hardyâs voice came over the speaker.

âDad! When did you get home?â

âJust arrived. Where are you fellows now?â

âWeâre downtown in the car. In fact, weâre headed for home.â

âGood. This case Iâm working on looks pretty tough and I may need your help. Iâll have to leave again first thing in the morning, so Iâd like to fill you in on the details this evening.â

âWeâll be there pronto, Dad!â

A short time later the convertible pulled into the driveway of the Hardysâ large, pleasant house on a tree-shaded street. The boys jumped out and hurried inside.

Fenton Hardy, a tall, rugged-looking man, was in the dining room having a cup of coffee. Seated at the table with him were Mrs. Hardy and the boysâ Aunt Gertrude, his unmarried sister.

The detective greeted Frank and Joe with a warm smile. âSit down, boys, and Iâll tell you what this case is all about.â

Mr. Hardy explained that he had been asked by a group of insurance underwriters to investigate a series of jewel thefts. The latest had occurred in New York the day before.

âWe heard a news flash on that, Dad!â Joe exclaimed.

âUndoubtedly all the thefts have been pulled by the same gang,â the detective went on. âAnd thereâs an odd feature. On every job, the guards or other persons involved seem to have lost their memory for a short period of time while the robbery was taking place.â

âYou mean they passed out?â Frank asked.

Fenton Hardy shrugged. âNone of them recalls passing out. But they all report a sensation of coming to, or snapping out of a deep sleep, as if they had lapsed into unconsciousness without realizing it.â

Gertrude Hardy, a tall, angular woman, pursed her lips and frowned shrewdly. âIf you ask me, they were gassed,â she declared. âSome kind of nerve gas, probablyâsquirted at the victims through a blowpipe.â

Frank and Joe tried hard not to grin. Their aunt had definite opinions and never hesitated to express them.

âThey may have been gassed,â Mr. Hardy agreed. âBut if so, itâs strange that police experts were unable to discover any traces in the atmosphere afterward.â

âMaybe the crooks sucked it all back into their blowpipes,â Joe said mischievously.

Aunt Gertrude gave him a withering look. âMaking fun of me, are you? Well, maybe you have a better theory, young man!â

Laura Hardy, a slim and pretty woman, exchanged a fleeting smile with her husband. Both knew that Aunt Gertrude loved to talk about detective cases with her brother and the boys, even though she pretended to disapprove of such dangerous work.

âMatter of fact, we got gassed ourselves tonight,â Frank put in quietly. He told about their chase of the black sports car, but glossed over the part about skidding across the road.

âHmm.â Fenton Hardy knit his brows. âDo you think the driver could have recognized youâmaybe from seeing your pictures in the paper?â

Frank shook his head. âI doubt it, although he may have glimpsed us in his rear-view mirror when we passed a street light. I think that when he spotted a car tailing him, he used the smoke screen to shake us.â

âWhy, that manâs a menace!â Aunt Gertrude blurted out indignantly. âWhy didnât you radio the police at once? Mark my words, youâllââ

The ringing of the telephone interrupted Aunt Gertrudeâs prediction. Joe jumped up to answer it.

âLet me speak to Fenton Hardy,â said a curt, muffled voice.

âWhoâs calling, please?â Joe asked.

âNone of your business! Just tell him to get on the phone if he wants to learn something important!â

Fenton Hardy strode quickly to Joeâs side and took the receiver. âAll right, Iâm listening.â

âAnother jewel heist has been planned. Itâs going to be pulled aboard a yacht named the Wanda. Sheâs due in at East Hampton, Long Island, late tonight or early tomorrow morning. Got that?â

âI have it,â the detective replied. âBut who is this speaking?â

âA friend. And donât bother trying to trace the call!â

There was a cutoff click at the other end of the line. Mr. Hardy hung up thoughtfully and told the boys what the informer had said.

âIâd better follow up that tip-off,â he added. âIâll drive down to East Hampton.â

âAre you sure thatâs wise, Dad?â Frank asked worriedly. âThe call may be a trick.â

âItâs a chance Iâll have to take, son.â

Mr. Hardy telephoned Suffolk County Police Headquarters on Long Island to report the tip. Before leaving the house, he suggested that the boys restudy the photo of Strang in his file, and also the typewritten data on the reverse side of it.

âMind you, we have nothing on him,â the detective said. âBut I think heâs one of the few jewel thieves in the country capable of master-minding a series of robberies like the ones Iâm investigating.â

âDo you want the police to take him in for questioning?â Joe asked.

âNo, that would only put him on guard. But I would like to know what heâs doing in Bayport!â

âWeâll keep an eye out for him,â Frank promised.

Mr. Hardy then placed a long-distance call to his top-flight operative, Sam Radley. Sam had flown to Florida with a charter pilot named Jack Wayne to wind up another case. Fenton Hardy instructed Sam to join him at East Hampton the following day.

Next morning, Frank and Joe ate a hearty breakfast of bacon, eggs, and homemade muffins, then started off in their convertible to pick up Chet Morton. After some grumbling, the stout boy agreed to help them search for the curious tiled square he had seen the night before. Frank pulled up on the dirt lane near the big oak tree.

âI donât know why I let you two talk me into this,â Chet complained as they started up the slope. âI canât seem to stay out of danger when youâre around.â

Joe laughed. âStop griping. You donât expect to hear any spooks in broad daylight, do you?â

When they reached level ground, Frank remarked, âSay, I see a house over there!â

Joe and Chet looked in the direction he was pointing. A large, weather-beaten mansion was visible through the trees some distance away.

âDidnât notice any lights over that way last night,â Joe said. âWonder if anyone lives there.â

âMaybe not,â Frank said. âLooks pretty run down.â

For half an hour the boys searched among the tall weeds and overgrown shrubbery. They failed to sight the tiled surface Chet had described, or to find Frankâs knife.

âSure you werenât just seeing things last night?â Frank asked Chet.

Joe chuckled. âMaybe just hearing things, too?â

Before Chet could reply, a voice barked out, âStand right where you are! Now turn around, all three of you!â

The boys whirled in surprise. A tall, hawk-faced man with a thin, prominent nose was standing among the trees watching them. He had one hand in his suit-coat pocket, as if concealing a gun.

Frank and Joe gasped. The man looked like the one in the photograph of Noel Strang their father had in his files!

CHAPTER III

The Purple Stone

âDONâT stand there gawking!â the man snarled. âWhat are you kids looking for?â

Chet gulped. âW-wellâuhâyou see, 1-last nightââ

âI lost my pocketknife,â Frank spoke up. âWe were trying to find it.â

âYour pocketknife, eh?â The man scowled at the boys suspiciously. âYou had no business nosing around here last night or anytime. This is private property. Now clear out!â

Chet, overcome with jitters, hastily started walking back to the car. Frank and Joe did not budge, and continued to stare at the man.

âYou heard me!â he said in a loud, belligerent voice. âBeat it! And donât come back!â

He took a few steps toward the Hardys and crooked his arm as if he were about to jerk his gun hand out of his pocket. Without a word, the brothers turned and followed Chet.

âThat is Noel Strang!â Joe whispered. âThink we should call his bluff?ââ

Frank shook his head. âNot now. Remember what Dad said.â

âHe may not own this property,â Joe argued. âIf he does, maybe we can find out what heâs doing here.â

âI intend to,â Frank said. âBut letâs try to do it undercover, without making him suspicious.â

Chet had already climbed into the car. He was sitting stiffly in the back seatâstill pale and nervous, but whistling off-key and trying to look casual.

Frank slid behind the wheel and Joe got in beside him. As they glanced back up the slope, the boys could see Strang watching them intently.

âOhâoh,â Joe muttered. âI just thought of something!â

âLike what?â Frank asked.

âIf heâs the one who used that smoke screen last night, he may recognize our convertible.â

âSmoke screen!â Chet gasped. In the rear-view mirror, Frank could see that the fat boyâs eyes were bulging with fear. âYou mean that guyâs a gangster?â

âNot exactly,â Joe said, as Frank turned the car around. âJust a notorious jewel thief named Noel Strang.â

Chet groaned as the Hardys told him the details. âOh, this is great! I donât want to get mixed up in another one of your cases! Youâd better take me home.â

The Hardys grinned. âChet, you know you eat up excitement as well as food,â Frank said.

âIt helps to keep your weight trimmed down,â Joe suggested.

âListen! Iâll probably lose ten pounds just worrying about this thief,â Chet retorted. âStrang may even send his men after us!â

Joe chuckled. âJust threaten to sit on âemâthatâll be enough of a scare.â

Frank suddenly looked troubled. âNow I just thought of something, Joe.â

âBad?â Joe glanced at his brother.

âNot good. That knife has my name engraved on it. If Strang finds the knife, he may connect us with Fenton Hardy.â

Joe gave a low whistle. âLetâs hope he doesnât find it!â

A short time later Frank swung up the graveled driveway leading to the Mortonsâ farmhouse. Chetâs pretty, dark-haired sister Iola was seated on the front porch with her blond, brown-eyed friend Callie Shaw.

Iola bounced up from the porch swing as the boys stepped from the car. âHi!â she exclaimed. âWaitâll you see the surprise Callie and I have to show you!â The girlsâ eyes sparkled with excitement.

Joe grinned at Iola, whom he considered very attractive. âSounds pretty important.â

âAw, itâs probably some new doodads for their charm bracelets,â Chet scoffed.

âLike fun!â Iola retorted. âItâll make you turn green with envyâI mean purple!â

As the boys followed the two girls into the house, Callie explained that she and Iola had been rock hunting the day before. With a giggle, she also whispered to Frank that Chet and Iola were rivals at rock hounding.

In the dining room, Iola went straight to the old-fashioned punch bowl on the buffet and took out a stone about the size of a grape. It was pale violet and roughly crystalline in form.

âFeast your eyes!â she said, waving the stone under Chetâs nose.

âWell, hold it still so I can see it.â The chubby youth stared in grudging admiration.

âItâs beautiful,â Frank said. âIs that an amethyst?â

Iola bobbed her head proudly. âA real one!â

âWe took it to Filmerâs Gemstone Shop this morning to make sure,â Callie added. âMr. Filmer identified it for us.â

Chetâs eyes bugged out in awe. âWow! A real jewel!â he gasped. âWhereâd you find it?â

Iola and Callie blushed with embarrassment. âWe donât remember,â Iola confessed.

âYou donât remember?â Chet echoed. âHow goofy can you get! Why, there might be a whole lode of amethysts around the spot!â

âBut we picked up oodles of stones in several places,â Callie explained. âThe light wasnât good in the late afternoon and we didnât realize that this one might be valuable.â

âWeâre not even sure which one of us found it,â Iola put in. âWe didnât get excited until we sorted the stones this morning.â

Chet was about to make a wisecrack when Joe happened to glance out the window.

âHey!â he yelled. âYour barnâs on fire!â

The others stared and gasped. Black smoke was billowing out through the open barn door!

âGood grief!â Chet shouted. âAnd Dadâs over at the vetâs this morning! Quick! Get some fire extinguishers and buckets of water!â

The five teen-agers dashed outside, followed by Mrs. Morton, who had hurried upstairs from the cellar when she heard their cries.

There was no sign of open flames from the barn, so Frank and Chet plunged inside to get a pair of fire extinguishers hanging on the wall. Joe and the girls, meanwhile, prepared to form a bucket brigade from the pump.

âOh, my goodness!â Mrs. Morton cried distractedly as she hovered outside the barn. âShall I call the fire department?â

âDonât bother, Mom!â Chet shouted back. âThis looks like a false alarm!â

Soon the smoke began to clear and the two boys emerged, grimy from the thick fumes. âA bucket of oil was burning,â Frank explained, coughing.

âSure beats me how it started,â Chet added. âI wouldnât think heavy tractor oil could ignite by spontaneous combustion.â

Relieved, they all trooped back to the house. Mrs. Morton provided soap and towels so Chet and Frank could wash in the kitchen. Joe and the girls returned to the dining room.

Iola went to pick up the amethyst but could not find it. âCallie, did you take our jewel outside with you?â she asked.

âNo, you left it on the table, didnât you?â

âI thought I did.â Iola hastily checked the punch bowl, then turned an anxious face to the others. âItâs not here!â

A frantic search followed, with Joe scrabbling on the floor and the girls going through every drawer and compartment of the buffet. The amethyst was gone! Frank and Chet heard the news as they came into the dining room.

âOh, fine!â Chet groaned. âFirst a fire, and now you girls lose the only valuable stone weâve ever found!â

Frank and Joe looked at each other with the same thought in mind.

âIâll bet that fire was a trick to get us out of the house!â Joe exclaimed.

âYou mean the stone was stolen?â Iola gasped.

âIâm afraid so,â Frank said. âBy the same person who set fire to that bucket of oil.â

Callieâs eyes glowed with a sudden recollection. âI heard a car start up down the road just as we came back to the house!â she said. âIâll bet that was the thief getting away!â

Chet plumped himself down in a chair. âBoy, this is turning out to be one swell day.â He grunted, then brightened. âGuess we may as well have lunch.â

Frank telephoned a report of the theft to the police and then called home to notify his mother that he and Joe would be lunching at the Mortonsâ.

Aunt Gertrude took the message. âBy the way,â she said, âTony Prito has called twice, trying to get hold of you and Joe. Wouldnât tell me what he wanted, but he did say it was urgent.â

âWhere can I call him?â Frank asked. âAt his dadâs office?â

âMmmâno, I believe he said he was phoning from the boat dock.â

âOkay, Aunty. Thanks.â

Frank and Joe apologized to Mrs. Morton for hurrying through the hearty lunch she served them. As soon as they had finished, the brothers excused themselves to go and find Tony Prito.

Tony, a dark haired, good-looking boy, was a close pal of the Hardys and they often went out on Barmet Bay with him in his motorboat, the Napoli. Frank and Joe drove quickly to the boat basin but could not see Tony anywhere.

âIâll bet heâs out in the Napoli,â Joe said, staring out across the harbor.

âProbably so.â Frank glanced up at the sunny sky and then at the gently white-capped blue waters of the bay. âLetâs get the Sleuth, Joe, and try to find him.â

âSuits me.â

The Hardys hurried off to the boathouse where they kept their own motorboat.

At that moment Tony was just driving up to the Mortonsâ house in his fatherâs pickup truck.

âHi, Chet! Have you seen Frank and Joe today?â he called to the stout youth, who had come out to the porch.

âSure. They had lunch here. Left about fifteen minutes ago, heading for the boat dock to find you.â

Tony suddenly went pale. âMan, I hope they donât go out in the Sleuth!â

âWhy not?â Chet asked, puzzled.

âHop in and Iâll tell you. Weâd better get there fast!â

Chet hardly had time to get into the cab before Tony threw the truck into reverse and backed up. As he swung the vehicle around and sped down the road, he explained, âI saw two tough-looking guys sneak out of Frank and Joeâs boathouse. Somehow I have a hunch those men were up to no good!â

âDid you recognize them?â Chet asked, wide-eyed.

âNo, but Iâm afraid those men may have sabotaged it!â

âDidnât you warn Mrs. Hardy and Aunt Gertrude?â

âGuess I should have,â Tony said ruefully. âBut I didnât want to alarm them.â

As the truck pulled up on the quay, Chet exclaimed and pointed toward the water. âThere they go now!â

The Sleuth, with two figures aboard, was put-putting out across the bay.

âWeâre too late,â Tony groaned.

The boys leaped out of the truck and began shouting and waving frantically to their friends. But the Hardysâ boat was too far out for the brothers to hear the cries.

Suddenly a loud explosion shook the Sleuth!

CHAPTER IV

The Jigsaw Face

THE force of the blast jerked the bow of the Sleuth up out of the water! Both its occupants were hurled overboard and the boat itself overturned. Smoke billowed from the scene.

âCome on!â Tony cried to Chet. âWe must get out there and pick them up!â

âWhereâs the Napoli?â Chet puffed as they ran along the quay.

âI left it tied up at the North Dock.â

People were already gathering excitedly along the waterfront. The two boys reached the North Dock and leaped into the motorboat. Chet cast off and Tony gunned the outboard into life. In a moment they were speeding out on the bay.

Chet, who was seated in the bow, shouted in relief, âLooks as if Frank and Joe are okay!â

The Hardys had been struggling in the water, but could now be seen clinging to their overturned craft. The Napoli came alongside.

âBoy, this is what I call service!â Joe said as he and Frank were hauled aboard.

Tony explained, âWe came to give you a warning.â

âTony, we came out here looking for you,â Joe replied. âYour boat wasnât in the basin.â

âNo, I took it out this morning and tied up at the North Dock when I came back.â

âWhat did you mean about warning us?â Frank put in.

Tony hastily told about seeing the two men sneak out of the boathouse. Just as he finished, a Coast Guard rescue launch reached the scene. Other boats were approaching also.

âEverybody okay?â the chief petty officer called out from the Coast Guard launch.

âTheyâre okay but plenty wet,â Chet replied.

âWhat happened?â the officer asked.

âSome kind of explosion in the forward compartment,â Frank told him. âWe suspect sabotage.â

The chief ordered his coxsân to maneuver the launch closer to the overturned craft. A hole had been blown in the hull near the bow, but the boatâs special flotation apparatus in the forward space had kept it from sinking.

âCan your friends tow the boat to a repair dock all right?â the chief asked the Hardys.

âWe can manage, if someone will give us a hand,â Tony spoke up.

âIâll help you, lads!â called a man from a nearby motor cruiser.

âIn that case, Iâd like you fellows to come back to the Coast Guard station with me and make a report,â the officer told Frank and Joe.

The Hardys transferred to the Coast Guard launch, which immediately sped off to its base. Meanwhile, Tony and Chet tackled the job of putting a towline onto the Sleuth, with the help of the man in the motor cruiser.

At the Coast Guard station Frank and Joe told their story to a lieutenant named Anson. âYouâre Fenton Hardyâs sons, arenât you?â he asked.

âYes, sir,â Joe answered.

âIs this sabotage connected with one of his cases?â

Frank hesitated. âWe think so, sir, but we donât know yet.â

Lieutenant Anson asked, âAny theories?â

âSomeone was trying to kill us, or at least scare us off our investigation,â Frank said. âMy guess is the bomb was detonated chemically in some way by the salt water. But I have a hunch it went off too soonâthe saboteurs hoped weâd be farther out in the bay.â

âRight,â Joe agreed. âIâll bet the blast was supposed to swamp the boat fast, drown us, and send all our evidence against them to the bottom. But luckily for us, the boat overturned and stayed afloat, giving us something to cling toââ

Lieutenant Anson took down their statements, then said, âFor the record, Iâll say youâre carrying out your own investigation. But please keep us informed.â

He had an enlisted man drive the boys back to their car. Frank and Joe went home, where Aunt Gertrude greeted them with clucks of disapproval.

âWell, I never! Itâs a good thing your mother has gone to the library board meeting!â Miss Hardy ordered the boys to take off their soaked shoes to avoid tracking up the carpet, then went on anxiously, âWhat happened? Did that crook youâre after make you walk the plank?â

Frank chuckled and gave her a damp hug, which Miss Hardy tried to fend off. âSlight accident, Auntyâa dunking we didnât expect.â

The boys had just changed into dry clothes when the telephone rang. Joe answered. The caller was Chief Collig.

âGot a report from the Motor Vehicle Bureau on that sports-car license number,â he said. âItâs registered in the name of Aden Darrow.â

âNever heard of him,â Joe replied.

âNothing on him in our files, either.â

âWhat about the address?â

âA street number in Eastern City,â Collig said. âI checked with the police there but they couldnât help. The whole streetâs been demolished for an expressway.â

âDead-end clue. Well, thanks a lot, Chief.â

A short time later Tony Prito and Chet arrived. They reported that the Sleuth had been safely towed to the repair dock. Frank telephoned to determine the cost of repairing the boat, then the boys gathered to discuss the dayâs events. Frank and Joe quickly told Tony about the case.

âYou figure the men who planted the bomb were working for Strang?â Tony asked.

âCould be,â Frank said. âEspecially if he found my knife and learned our name.â

âIâll bet he recognized us last night!â Joe put in.

âHow about that sneak who took Iola and Callieâs amethyst?â Chet asked. âMaybe Strang did that too. You said heâs a jewel thief.â

Frank frowned. âThatâs true. But heâs a big-time operator. I doubt if the amethystâs worth enough to tempt him.â

âAnyhow, Strangâs definitely got business in this area,â Joe said. âDo you think he could be hiding out at that old houseâthe one we saw him near this morning?â

âCould be,â Frank said.

Tony asked where the place was located. When Joe told him, Miss Hardy exclaimed, âWhy, thatâs the old Perth mansion!â

âDo you know who lives there?â Frank asked.

âNo one, far as Iâve heard,â she replied. âHasnât been occupied for years. The place had what you might call a sinister reputation.â

âHow come?â Joe inquired.

âSeems someone died there under mysterious circumstances. Donât recollect just who. But there was talk about the place being haunted.â

âHaunted?â Chet swallowed and turned pale.

Miss Hardy sniffed. âAll stuff and nonsense. Some folks will believe anything. That was years agoâeven before you boys were born.â

âTell us some more, Aunty,â Frank urged.

Gertrude Hardy settled into her favorite chair. âWell, the house originally belonged to a man named Jerome Perth. Not a nice person at all, from what folks used to say.â

âWho was he?â Frank asked.

âSome sort of big business tycoonâbut a shady operator. People accused him of all sorts of thingsâstock swindles, patent infringements. I donât know what all. But I guess no one ever pinned anything on him.â

âMust have been pretty slick,â Tony remarked.

âOh, he was,â Miss Hardy agreed. âAnd he made a lot of enemiesâin fact, some of the people heâd cheated even tried to kill him. Finally he retired to that mansion he built and lived there in fear of his life.â

âSo his swindles didnât bring him any happiness,â Joe remarked.

âNo, indeed. I recall hearing he had his study on the ground floor fitted up with a bed and hardly ever stirred out of that one room.â

âBut you still donât remember who died there under mysterious circumstances?â Joe said.

Aunt Gertrude shook her head. âSome relative, I think. But I donât recall the details.â

Frank, meanwhile, had a sudden hunch. He telephoned Iola Morton to ask if anyone else had been in the gemstone shop when the girls showed the proprietor their amethyst.

âWhy, yes, there was,â Iola replied. âAnother customer came in right after we did. I remember he asked us where we had found our stone.â Suddenly Iola gasped. âOh! You mean maybe he was the one who stole our amethyst?â

âCould be,â Frank said. âHe might have shadowed you back to your house. Is Callie still there with you?â

âSure. Want to talk to her?â

âWeâll come out.â

Five minutes later Frank, Joe, and Chet were on their way to the farm in the Hardysâ convertible. Tony had to go back to work at his fatherâs construction company.

When the boys arrived at the Mortonsâ house, Frank carried in his fatherâs facial identification kit. Besides an illuminated viewing screen, the kit contrained strips of film showing hundreds of different hairlines, eyes, ears, noses, chins, eyeglasses, and hats.

Iola and Callie were fascinated as the Hardys began asking them to describe and identify the features of the stranger at the gem shop.

âItâs like putting together a jigsaw puzzle!â Callie exclaimed.

Bit by bit, the film strips showing the manâs features were laid together over the viewing screen until a whole face had been assembled.

âFor Peteâs sake!â Joe exclaimed. He and Frank stared at each other. âThatâs the guy we picked up unconscious last night!â

Chet peered over their shoulders, open-mouthed with surprise. âIt is for a fact!â

âJoe,â Frank said, âsuppose you take that face to the gem shop and ask Mr. Filmer if he knows the man.â

âOkay. How about you?â

âI want to go to the Bayport Times office and see if I can dig up any stories on the Perth mansion from their back files.â

Joe dropped his brother off at the newspaper office and a few minutes later pulled up in front of Filmerâs Gemstone Shop. He carried the kit inside and spoke to the proprietor.

Mr. Filmer, a skinny man with thick bifocal eyeglasses, seemed oddly nervous. âIâuhârreally donât recall anyone else being in the shop when Iola and Callie were here,â he stammered.

âPlease try to remember,â Joe begged.

âIâm afraid I canât.â

âAll right. At least let me show you a picture of the manâs face and see if youââ Suddenly Joe broke off. The door to the back room was ajar and he had just seen it move slightly.

Someone was eavesdropping behind the door!

âSo thatâs why Filmer wonât help me!â Joe thought. âIâll bet heâs afraid of the person hiding back there!â

The young detective wondered what to do. If he asked Mr. Filmerâs permission to look into the back room, it would forewarn the eavesdropper. But if he acted on impulseâJoe darted behind the counter and yanked open the door.

A tall, sandy-haired man, who looked like the one in the picture, streaked across the back room toward a window! Joe rushed forward and lunged at him. The stranger grabbed a stool and hurled it at Joe.

The stool struck Joe on the temple and he sank to the floor unconscious!

CHAPTER V

Spook Hound

As JOE regained consciousness, he felt something cold and damp on his forehead. He was propped in a corner of the gem shopâs back room and Mr. Filmer was bending over him, applying a wet towel to the bruise.

âFeel all right?â Mr. Filmer asked anxiously.

âIâI guess so, except for a sore head.â

âDear me! You have quite a lump there!â

âNever mind that.â Joe struggled to his feet. âWhat about that guy who slugged me with a stool?â

Mr. Filmer pointed helplessly to an open window. âHe got away and ran off down the alley.â

âI suppose heâs the one who was here when Iola and Callie brought in their amethyst?â Joe said, repressing an angry comment.

Mr. Filmer reddened. âIâm terribly sorry I had to lie to you. He was hiding back here all the time, listening. I was too frightened to talk.â

âWell, heâs not here nowâso who is he?â

âI really donât know,â Mr. Filmer said, looking bewildered. âHe often drops into the shop to talk to the local rock hounds, and always seems especially interested in amethysts. Thatâs about all I can tell you.â

âWhen did he get here?â Joe asked.

âJust a few minutes before you did. He asked me if anyone had been inquiring about him. When I said No, he warned me to keep my mouth shut or else heâd have me beaten up. Then he saw you coming and ducked into the back room.â

âIf he ever shows up again,â Joe said, âwill you try to notify the police right away?â

âI certainly will!â Mr. Filmer nodded vigorously, eager to make amends.

Joe thought of trying to lift some fingerprints, but he remembered that the man had been wearing gloves. Before leaving, Joe telephoned a report of the incident to Chief Collig.

When Joe reached home, his mother insisted upon applying a soothing dressing to his swollen temple. Aunt Gertrude hovered close by, supervising the treatment and muttering darkly about the dangers of detective work. Joe merely grinned at her sharp comments.

Soon afterward, Frank arrived home. He took one look at Joe, who was curled in an easy chair watching TV, then let out a whistle.

âWhereâd you get that decoration?â

âI connected with a stool,â Joe said wryly. He told Frank what had happened at the gem shop and added, âI still canât figure how that man knew weâd go there to check on him.â

âProbably followed the same line of reasoning we did,â Frank replied. âThe girls just picked up the amethyst yesterdayâso the shop is the only place where an outsider could have learned about their find. Besides, he had quizzed Iola and Callie about the stone, and you say Filmer knew of his interest in amethysts.â

âIn other words, he guessed we might put two and two together. Rather than take any chances, he decided to bulldoze Filmer into silence.â

Frank nodded, and Joe added, âNow how about telling me what you found out.â

âI got the full story,â Frank said eagerly. âThe person who died at the Perth mansion under mysterious circumstances was Old Man Perthâs nephew. Must have been quite sensational. The Times had a flock of old write-ups on it.â

Joeâs eyes brightened with interest. âWhat happened?â

âWell, the nephewâClarence Perthâmoved into the mansion after Jerome Perth passed away from a heart attack. He took over the old manâs bedroom-study. But he lived only a few days to enjoy his inheritance.â

âHow come?â

âOne night, long after midnight, the servants heard him scream in terror,â Frank continued. âThey broke into the room and found him lying on the floor with his skull fractured. And get thisâjust before he died, the nephew muttered something which sounded like âthe floorâ!â

Joe gave a whistle. âWow! When Chet hears that, heâll be positive it was a ghost that screamed at us last night.â

âThereâs more,â Frank went on. âBoth the door and the windows of the room had been locked from the inside and none of them brokenâso there was no way a killer could have entered the room or escaped.â

âHow about trap doors or trick wall panels?â

Frank shrugged. âThe stories said the police looked for secret exits but didnât find any. Of course, criminal-detection methods then werenât what they are today.â

âWhat about the ghost angle?â Joe queried.

âThere are several follow-up news items. They said that a number of persons had reported seeing a ghostly figure prowling about the Perth estate.â

âHumph! No doubt thereâll always be gullible simpletons!â said a peppery voice. Aunt Gertrude planted herself in an easy chair and began darning socks. âDonât mind me.â She sniffed. âJust go right on with your wild talk.â

Frank and Joe exchanged grins, knowing their aunt was eager to hear more. She looked gratified when Frank repeated the information he had gleaned from the Bayport Times.

âYes, I remember now about Perthâs nephew,â Miss Hardy said reminiscently. âPoor fellow! Almost seemed as if Fate had marked him out to pay for his uncleâs misdeeds.â

At dinner Frank and Joe were silent and thoughtful. Neither believed that the weird screams they had heard near the Perth mansion could have been made by the nephewâs ghost. Nevertheless, it was an eerie notion!

âIâd like to go back to that mansion,â Joe said as the family finished dessert. âI have a hunch weâll find some answers thereâabout the ghost and Strang too.â

Frank agreed. âWeâll go as soon as itâs dark.â

Two hours later the brothers climbed into their convertible and headed toward the outskirts of Bayport. Their tires hummed in the still, moonlit night air and wispy clouds covered the sky. When they turned onto the dirt lane, Frank switched off their headlights and soon afterward pulled in close to a screen of shrubbery.

âBetter take our flashlights,â Joe murmured.

The boys got out and headed up the slope. In the distance they could see a few gleams of light from the house.

âCome on! Donât argue with it!â Frank muttered

âSomeoneâs in the haunted house!â Joe remarked. âMaybe Strang. Weâd better watch our step!â

The Hardys threaded their way among the trees and underbrush. Suddenly a ferocious snarl made them whirl to the left.

A huge, savage-looking hound stood facing them, its eyes glowing in the dark like coals of fire! Again it snarled, and seemed about to spring at the two intruders!

âCome on! Donât argue with it!â Frank muttered. He started to back away hastily, but Joe clutched his arm.

âWait, Frank! That thingâs not aliveâitâs just a mechanical dummy!â

Incredulous, Frank did a double-take. Then he realized that Joe was right. âWell, Iâll be a moldy dog biscuit!â he gasped. âThat hound sure looks real enough to bite your head off!â

âWe must have crossed an invisible beam that made it light up and snarl,â Joe surmised. He reached out a hand to touch the device, as if to reassure himself that the âdogâ was not flesh and blood.

âHold it, Joe!â Frank jerked his brotherâs hand away. âThat thing looks like metalâit may be electrically charged.â

Stripping off his belt, Frank held the leather end and swung the buckle lightly against the mechanical hound. A hissing blue-white spark illuminated the darkness as metal touched metal!

âWow!â Joe gasped. âThat really would have given me a jolt! Say, Frank, do you suppose the guy we found here could have been shocked unconscious by some electrified gadget?â

âSounds like a good guess. And that gives us another reason for watching our step.â

More cautiously than ever, the Hardys approached the old mansion. The house, covered with fading clapboards, was fronted by a low veranda and topped off with turrets and decaying latticework. Ragged clumps of shrubbery grew close to the walls.

âLetâs try those lighted windows on the first floor,â Frank suggested.

The boys crept close enough to peer inside. Bookshelves, a desk, chairs, a bureau, and a bed lined the walls of the room.

âThis must have been Jerome Perthâs bedroom-study,â Joe whispered.

He brought his face up closer to the pane for a better view, then gave a cry of astonishment. âFrank, look! The room has no floor!â

CHAPTER VI

Symbol in Brass

FOR a moment Frank thought his brother must be joking. Then he, too, put his face to the window-pane. Beneath the roomâs furniture he could see only gaping darkness!

âThis is crazy!â Frank muttered. âThat furniture canât just stand in mid-air!â

âIf only we could see better,â Joe said, flattening his nose against the glass in an effort to peer downward. Suddenly Frank gave a warning hiss and yanked Joe into a crouched position.

âWhatâs wrong?â Joe whispered.

Frank pointed off beyond the rear of the house. In the distance a tiny light could be seen moving among the trees. The boys shrank back into the shadows of some shrubbery.

As they waited, Joeâs eyes fell on what looked like an old coin. It was lying on the ground in the patch of light outside the window. Joe reached out and pocketed it.

Meanwhile, the oncoming beam was zigzagging slowly about the grounds. Minutes went by. A night breeze sighed eerily among the hemlocks and cypresses. Bit by bit, the light moved closer to the boysâ hiding place.

Frank strained his eyes in the darkness. Suddenly his scalp prickled. âJoe!â he gasped. âDo you see what I do?â

âI sure do!â Joe gulped.

The light was being carried by a ghostly white-robed figure! But common sense told the boys the figure must be human.

âThis is our chance to lay that spook story to rest once and for all,â Frank whispered.

Joe glanced at his brother. âYou mean we rush the ghost?â

âRightâbut not yet. Wait till I give the word.â

The white figure flitted along, pausing every so often amidst the tall underbrush. For a time it seemed to be approaching the house. Then the light moved off in another direction.

Frank put his mouth close to Joeâs ear. âLetâs sneak up and take Mr. Spook by surprise now!â

Silent as shadows, the Hardys darted out from the shrubbery. Moving with swift steps, they closed in toward the phantom figure. But Joe, overeager, caught his foot in a tangle of underbrush and thudded to the ground.

The âghostâ whirled, evidently startled by the noise. The flashlight it was carrying raked the two boys, then winked out abruptly. An instant later the figure had slipped away into the darkness!

Frank halted only long enough to make sure his brother was unhurt, then raced in pursuit. Joe scrambled to his feet.

By now the white-robed figure was nowhere to be seen. Then Joe suddenly glimpsed something pale among the trees. Was the spook trying to evade them by doubling back toward the house? Joe sprinted to intercept it.

He saw the phantom figure pass between two trees. Instantly the faint ringing of an alarm bell could be heard from inside the mansion!

âThere must be another electronic-eye beam between those trees!â Joe realized.

Floodlights blazed on around the house. The front door burst open and three men dashed outside. The ghost, meanwhile, had veered to the left and was disappearing into the darkness againâthis time toward the road, but away from the Hardysâ car.

Joe halted, uncertain what to do next. If he continued the pursuit, he would risk being cut off by the men from the house before he could get back to the convertible.

âFor all I know, they may be the ones who blew up our boat!â he said to himself.

As the men came closer, Joe made a fast decision and darted off among the trees. A moment later he was startled by a rustle of shrubbery close by. A shadowy figure was running alongside him! âYou okay, Joe?â

âYes. But wow! Donât give me heart failure like that!â

The sounds of pursuit grew fainter and presently the two boys reached sloping ground and headed toward their car.

Both boys hopped into the convertible. Frank keyed the starter and the engine came alive with a roar. Spinning the wheel, he sent the car zooming down the lane. âTalk about fast getawaysâ!â Joe panted as they reached the highway.

âDid you get a look at those men from the house?â Frank asked.

âNot too good a look, but I think one of them may have been Noel Strang.â

As the brothers came in the kitchen door of the Hardy home, they heard a loud buzz from the basement.

âThe short-wave radio signal!â Frank exclaimed. He and Joe hurried downstairs and switched on the powerful set which the Hardys used for secret communications.

âFenton H. calling Bayport. Come in, please.â The last words swelled to stronger volume as Joe tuned the receiver.

âBayport to Fenton,â Frank said. âWe read you loud and clear!â

âGood! I hoped Iâd catch you boys in.â

âHowâd that telephone tip pan out?â Frank inquired eagerly.

âIt hasnât so far,â Mr. Hardy reported. âThe Wanda didnât arrive until six this evening. Its passengers are all wealthy people, and thereâs a fair amount of jewelry aboard. But as yet we havenât turned up a single clue that might indicate a robbery is planned.â

âDo you think the tip was phony?â

âToo early to tell yet. The police have a dragnet out but they havenât spotted any likely suspects. Of course itâs possible the jewel thieves called off the job for some reason.â

âDad, itâs also possible the gang wants you stymied there in East Hampton while they prepare to pull a job somewhere else,â Frank pointed out.

âThatâs what Iâm afraid of,â Mr. Hardy agreed. âMeanwhile, Sam and I canât do much. Whatâs the picture there in Bayport?â

Frank rapidly briefed his father on the dayâs developments. Mr. Hardy was stunned to hear about the bombing of the Sleuth and the attack on Joe at Filmerâs Gemstone Shop. Also, he was intrigued by the Motor Vehicle Bureauâs report.

âIâm sure Iâve heard that name, Aden Darrow, but I canât place it,â the detective said. âTry checking my criminal file.â

After a hasty conference with his operative, Sam Radley, Mr. Hardy added, âSon, the way things are popping there in Bayport, I think Sam had better fly back and help you boys with your investigation. Iâll get hold of Jack Wayne. He should be able to land Sam there by midnight.â

âOkay, Dad. Weâll meet Sam at the airport.â

After signing off, Frank and Joe hurried upstairs to their fatherâs study. A thorough check of his file revealed no criminal listed under the name of Darrow.

âDad mustâve been mistaken,â Joe concluded.

Mrs. Hardy and Aunt Gertrude were watching a movie on television. The brothers joined them.

âI suppose you boys would like a snack,â their aunt said after the program ended.

âWe wouldnât object,â Frank replied with a grin.

As Miss Hardy went out to the kitchen, Joe suddenly remembered the coin he had picked up near the mansion window. As he examined it the young sleuth gave a cry of excitement.

âFrank! Take a look at this!â

The coin appeared to be a brass lucky piece. On both sides it bore the design of a dragon!

âWow! The same design Chet saw on that tiled square!â Frank exclaimed.

The boys began to discuss their new clue excitedly. Mrs. Hardy also looked at the lucky piece and pointed out the design of a violet above the dragonâs head. Soon Aunt Gertrude returned to the living room, carrying a tray of sandwiches, cookies, and milk. She, too, became curious and asked to see the brass coin.

âWhy, this belonged to old Jerome Perth!â she announced triumphantly.

âHow do you know?â Joe asked.

âFrom the designâthatâs how,â Aunt Gertrude retorted. âIt was his personal trademark.â

âAunty, youâre wonderful!â Frank exclaimed.

âThat swindling old reprobate used to hand out these pieces right and left,â she went on. âEspecially when anyone asked him to contribute to charity! Used to say these would bring the holder luck, which was more important than money.â Miss Hardy sniffed. âThe dragon was appropriate!â

âWell, since this is the design Chet describedâthe one he saw on the tiled squareâwe know he didnât imagine it,â Joe said to Frank.

âBut we still donât know its purpose,â Frank pointed out.

Mrs. Hardy and Aunt Gertrude were keenly interested when they heard of Chetâs experience. Mrs. Hardy puckered her brow thoughtfully. âGertrude, wasnât there once a summerhouse near the Perth mansion?â she asked.

âI believe there was, Laura. Seems to me it fell into neglect and was torn down. Why?â

âI was just wondering if that tiled surface might have been the floor of the summerhouse.â

Joe snapped his fingers excitedly. âIâll bet youâve hit it, Mother!â he exclaimed.

Frank nodded in agreement. âBut in that case, why couldnât we find it this morning?â he mused.

Before anyone could answer, the TV late news came on. âA bulletin just handed me,â said the newscaster, âstates that a daring jewel robbery was pulled in Chicago at ten oâclock tonight. More than one hundred thousand dollarsâ worth of uncut gems were stolen from the Spyker Jewelry Company. No further details as yet.â

âWow! That phone tip of Dadâs must have been a fake!â Joe exploded. âIâll bet Strang wanted to make sure Dad was safely sidetracked on Long Island before the gang pulled this new job!â

Frank sprang to his feet. âCome on, Joe! We can do some more detective work tonight!â

CHAPTER VII

A Fast Fade-out

âWHAT do you have in mind, Frank?â Joe asked.

âYou werenât sure Noel Strang was one of those men at the mansion tonight,â Frank explained, âbut we do know we saw him this morning.â

âSo?â

âIf he was involved in this latest jewel robbery, he must have flown to Chicago. Itâs the only way he could have reached there in time. Maybe we can check that out at the airport.â

âSmart idea!â Joe agreed. âWaitâIâll get the photo of Strangâwe can use it if we need to ask the airlinesâ personnel whether or not theyâve seen him.â

The Hardys reached the airport a few minutes before twelve. Joe said, âLetâs start by checking the passenger lists for todayâs flights to Chicago.â

âStrang wouldnât have used his own name if he were en route to commit a crime,â Frank objected.

âMaybe not, but how about one of his aliases?â Joe pointed to a paper with typewritten data pasted on the reverse side of Strangâs photo.

âHey! Thatâs a thought!â

At each of the airline desks, the boys asked to see passenger lists for all flights to Chicago since that morning. Neither Strangâs name nor any of his known aliases was listed.

Joe showed one desk clerk the photo of Strang, but the man shook his head. âAll the airline employes who are here now came on duty within the last hour.â Then he pointed to a porter who was lounging near a flight gate. âYou might ask that skycap over there. And try Benny at the newsstand.â

âThanks. Weâll do that.â

The boys showed their photograph to the porter and the newsstand operator. Neither recalled seeing such a man.

âHow about charter flights?â Joe asked, âLetâs check on that at the information desk.â

The attendant on duty told the boys that they would have to inquire about this at the control tower. âThatâs where the flight plans are filed,â he explained.

Before the Hardys could visit the tower, Joe spotted a plane coming in. âSkyhappy Sal!â he exclaimed.

This was a charter ship of the Ace Air Service, operated by Jack Wayne. Jack was a veteran pilot who often flew assignments for Fenton Hardy. The brothers were soon shaking hands with Jack and his passenger, Sam Radley.

âGood flight?â Joe asked the wiry investigator.

Sam nodded. âFast and smooth. Your dad thought you boys might brief me right away so we can plan some action.â

âWe can start now,â Frank told him, then gave an account of the events that had taken place in Bayport. He told of the jewel robbery in Chicago, and added, âJoe and I were about to ask the tower if Strang might have taken off for Chicago on a charter flight.â

âI can do that,â Jack offered. âI know the dispatcher.â

âSwell,â said Frank. âHereâs a photo of Strangâone of the men in the tower may recognize him, if he took a special flight out of here today. In the meantime, thereâs something the rest of us can be doing.â

âWhatâs that?â Radley asked.

âCheck the airport parking lot and see if Strangâs foreign sports car is here.â

âGood thinking, Frank,â Radley said approvingly. âYour dad will tell you that a smart detective never takes anything for granted.â

While Jack Wayne started off to the control tower, the Hardys and Sam Radley headed for the parking area. Although it was now past midnight, there were still several cars on the lot.

As Sam and the boys began their inspection tour, a man stepped into view from between two rows of parked cars. Bull-necked and powerfully built, he had crew-cut hair and was wearing a loud sports jacket. At sight of the detectives, he hastily turned and retreated.

Sam Radley was startled. âThat was Duke Makin!â he whispered.

âThe racketeer and con man?â Joe asked, having heard his father mention the name.

âYes,â Sam replied. âI wonder what heâs doing here.â His sleuthing instincts aroused, the detective strode forward to investigate. Frank and Joe followed eagerly.

Suddenly an engine roared and a car came zooming out of the darkness. Sam and the Hardys had to leap out of the way as it screeched past!

âThatâs Strangâs sports car!â Frank shouted.

Makin was hunched at the wheel. A figure appeared to be huddled in the space behind the front seat, but the car whizzed by too quickly for a clear view. It swung out onto the road.

âCome on! Letâs follow him!â Frank urged.

The Hardys and Radley ran to the boysâ convertible, leaped in, and took off. But the chase seemed hopeless from the start. Makin, speeding recklessly, already was out of sight.

Frank gunned the convertible along for a few miles, but after they had passed several crossroads and turnoffs, all three agreed to abandon the pursuit as hopeless. Glumly, Frank headed back to the airport.

âWhat do you suppose Makin was up to, Sam?â he queried. âThink he could be in with Strang on the jewel robberies?â

Radley frowned and shrugged. âMust be some kind of tie-up, if heâs using Strangâs car. Trouble is, we donât even know for sure that Strangâs involved in the robberies.â

âLooked to me as if someone was hiding in the car,â Joe remarked. âMaybe that was Strang himself, trying not to be spotted.â

âCould be,â Radley agreed. âBut if so, why was he hanging around the airport parking lot at this time of night?â

When they arrived back at the airfield, Jack Wayne had important news. A charter planeâowned and piloted by a man named Al Hirffâhad taken off at 9:37 P.M. The flight plan listed its destination as Chicago, and the ship was carrying a passenger named Norbert Smith.

âOne of the tower operators was down on the field at the time,â Jack went on, âand he saw the passenger getting aboard. He says the guy looked just like this photograph of Strang!â

âNow weâre getting somewhere!â Joe exclaimed. âFor one thing, Strang wasnât the fellow hiding in his own car.â

âDo you know this man Hirff?â Frank asked Jack.

âIâve seen him,â the pilot replied. âHe rented hangar space here about a week before I flew Sam down to Florida.â

âJack,â said Radley, âcould you stick around here and let us know when the plane gets back?â

The pilot nodded. âSure. I have a cot in the office. Maybe I can get chummy with Hirff and pick up some information for you.â

âGood idea,â said Frank. âOne thing more, Jackâkeep an eye out for a black foreign sports car with a dented trunk. It may come here to pick up Strang when he gets back.â

âWilco!â the pilot promised.

Radley was to bunk in the Hardysâ guest room overnight. As they drove home, the boys discussed the situation with him.

âThe plane took off at 9:37,â Joe mused. âAnd the robbery took place at ten oâclock. Itâs a cinch Strang couldnât have made it to Chicago in time to pull the job!â

âMaybe he planned it that way,â Frank reasoned, âso heâd have a clear alibi in case his movements were checked. He could have had confederates steal the jewels. Then Strang showed up in Chicago immediately afterward to take charge of the loot and give the robbers a fast lift out of town.â

âYou may have the answer,â Radley agreed.

When they arrived home, Mrs. Hardy greeted them with the news that her husband had radioed again. âHe heard about the Chicago jewel robbery right after you left Long Island, Sam. He wants you to contact him at once.â

Radley and the boys hurried downstairs and warmed up the transmitter. Soon Fenton Hardyâs voice came over the speaker. Frank and Joe quickly reported the latest developments.

âGreat work, sons!â the detective congratulated them. âThis is the first solid clue weâve had that may link Strang with the jewel thefts.â

âWant us to have him picked up for questioning if he comes back to Bayport?â Frank asked, taking the microphone from Joe.

âNo, the local police would have no jurisdiction. Anyhow, theyâd need a warrant from Chicago,â Mr. Hardy replied. âBesides, unless Strang were foolish enough to be carrying the loot with him-which Iâm sure he isnâtâwe still have no real evidence against him. Until we do, thereâs no sense tipping our hand.â

âHow about me, Fenton?â Sam Radley put in.

âIâll probably need your help to cover all the angles in Chicago. Tell you what, Sam. If Strang is back in Bayport by eight tomorrow morning, stay there and work with the boys. Otherwise, hop the eight-thirty commercial flight to Chicago and Iâll meet you at OâHare Airport. Tell Jack to stick around and give the boys a hand.â

Radley breakfasted early with the Hardys next morning, then the brothers took him to the airport. Hirffâs plane still had not returned, so Radley boarded the eight-thirty flight to Chicago.

Frank and Joe drove home and looked up Duke Makin in their fatherâs crime file. They learned that Makin had served time on three different convictions, and recently had been released from Sing Sing. Since then, so far as the dossier showed, no charge was pending against him.

Next, Frank called a real-estate agent who was a friend of Mr. Hardyâs and learned that the Perth estate had been handled by a realtor named Cyrus Lamkin. The boys drove to his office.

Lamkin sat at an old-fashioned roll-top desk. He was a pudgy white-haired man, whose vest was littered with cigar ash. âYouâre the Hardy boys, eh?â he said, rising to shake hands. âFine man, your father! What can I do for you?â

Frank asked guardedly if he could tell them the present status of the Perth mansion.

âWhy, I sold that just a few months ago,â Lamkin replied. âGood price, too. I imagine the owners were glad to get that white elephant off their hands! Theyâre distant relatives of the original owner. Live out in Ohio.â

âWho bought it?â Joe asked.

âMan named Aden Darrow.â Frank and Joe gave a start of surprise as Lamkin went on, âHeâs rather quick-tempered, but a very brilliant man apparently. Used to be a professor at Western State University.â

The Hardys looked at each other in amazement. Why would a college professor associate with a known crook like Strang?

Lamkin went on, âFunny how a piece of property can suddenly arouse interest in the real-estate market,â he mused conversationally. âTake that Perth place. Vacant for years. Then Darrow comes along and buys it. And now you lads are asking about the place. Second inquiry Iâve had in just a few days.â

âYou mean someone else besides us has been asking about it?â Frank inquired.

âYes, a prospective tenant came in the other day. He wanted to rent it.â

âSomeone local?â Joe asked.

âNo, from New York.â Lamkin paused to consult his calendar pad. âA Mr. Delius Martin.â

Again Frank and Joe were startled. The name was one of Duke Makinâs aliases!

After a short further conversation with Mr. Lamkin, the boys thanked the realtor and went out to their convertible.

âWhat do you make of it, Frank?â Joe said.

âNothingâthe puzzleâs getting more complicated all the time. A college prof rents the place, a notorious jewel thief moves in with him, and now we have to fit Makin in somewhere!â

The boys decided to check into Darrowâs background. But first they drove to the repair dock to see how work was progressing on the Sleuth. The manager promised to have the boat ready in three days.

Frank and Joe spotted the Napoli moored nearby. They were hailed by Tony Prito, who suggested they all go for a brief swim.

âHow about it?â Joe said, turning to his brother. âOur trunks are in the car.â

âOkay with me!â

Tony took the Napoli down the bay a short distance and they anchored at a pleasant spot in a sheltered cove. A cabin cruiser lay at anchor not far away. Frank and Tony took a quick plunge, then climbed back aboard to sun-bathe. Joe continued swimming by himself.

Like a seal, Joe cut his way down through the cool, refreshing water. Then he swirled back toward the surface.

Suddenly he felt himself seized from underneath. A brawny arm clamped itself around his neck in a choking grip and pulled him down!

CHAPTER VIII

Rock Houndsâ Shadow

JOE struggled desperately. He had already used up most of the air in his lungs even before he was attacked. Now he was being gripped beneath the surface, unable to call or signal for help!

Joe kicked and threshed, but he could not free himself from his attackerâs iron grip. The only result was a tightening of pressure against his Adamâs apple and a vicious jab in the ribs. When Joe tried to squirm around to face his assailant, the man rolled with him.

Joeâs lungs were soon near the bursting point. If only he could reach the surface!

Aboard the Napoli, Frank began to worry. âWhatâs Joe doing down there?â he muttered.

âMaybe he met a mermaid,â Tony quipped lazily.

As Frank scanned the waters, he noticed an uprush of air bubbles about a hundred yards away. Wordlessly, he plunged over the side.

Cutting his way downward, Frank peered intently through the wavering transparent greenness. His heart pounded at what he saw. Joe was helpless in the grip of a goggled frogman!

As Frank stroked swiftly toward them, the frogman released his victim and swam off.

âGood grief! I hope Iâm not too late!â Frank thought frantically.

Joe was limp, his head sagging as he slowly floated upward. Frank grabbed him under the arms and hauled him to the surface.

âTony! Give us a hand!â Frank shouted as he broke water.

Tony had been watching anxiously for a sight of the Hardy boys. At Frankâs call, he sent the Napoli gliding toward them. In a few moments they had Joe safely aboard.

âGet back to the dock! Fast!â Frank exclaimed. He positioned Joe as best he could in the bottom of the boat and quickly began applying mouth-to-mouth resuscitation.

The Napoli went planing over the water toward shore. The jouncing made Frankâs efforts doubly difficult, but by bracing himself against the side he managed to hold Joe fairly steady.

Tony cut the engine and yelled for help as he brought the boat alongside the dock. Four men assisted the boys in lifting Joe out of the Napoli, then laid him full length on the dock. Frank quickly resumed mouth-to-mouth resuscitation.

âIâve called an ambulance!â someone shouted.

But Joe was already reviving. Frank breathed a silent prayer of thanks.

âBoy! You sure had a close call!â Tony said, squatting down beside Joe.

âYouâre telling me.â Joe grinned weakly. âI mustâve swallowed half of Barmet Bay!â

By the time the ambulance arrived, Joe was on his feet. He allowed the intern to examine him but refused to be taken to the hospital.

âNothing doing. Iâm okay,â he insisted.

âWell, I canât force you.â The intern grinned and turned to Frank. âAt least take him home and put him to bed for a while.â

Once they were seated in the convertible and the ambulance had departed, Joe protested, âListen, Iâm not sleepy! Why should I go to bed?â he argued. âThen weâd have to tell Mom what happened. And think of the fuss Aunt Gertrude would make!â

âOkay, if youâre sure you feel all right.â

As the boys walked back to the dock, Joe said, âThe frogman who attacked me must have come from that cabin cruiser in the cove,â he reasoned.

âI think that cruiser pulled out before Frank and I started sun-bathing,â Tony objected.

âJoe could still be right. The cruiser could have left and arranged to pick up the frogman somewhere else,â Frank pointed out. âItâs a cinch he couldnât have been lurking on shore, just waiting for us to show up. We didnât even know, ourselves, that weâd be going to that particular spot to swim.â

âI guess youâre right,â Tony agreed, frowning thoughtfully. âMustâve been just bad luck. The cruiser spotted us, and whoever was aboard decided this was a perfect chance to nail at least one of the Hardys.â

The boys boarded the Napoli and made a quick scouting trip back to the cove. The cruiser was nowhere in sight. Neither Tony nor the Hardys had paid enough attention to the craft to be able to identify it. Nor had Frank seen the frogman clearly enough to provide the police with a useful description.

The boys dressed aboard the Napoli and headed back to the dock. Frank and Joe then said good-by to Tony and drove home. Chet Mortonâs tomato-red jalopy was parked in front of the house. A girl was seated in one of the porch rockers.

âThatâs Iola!â Joe exclaimed as they drove up.

She came running to meet them as they got out of the car. âOh, thank goodness!â Iola said excitedly. âI was afraid you might not get back in time!â

âSomething wrong?â Frank asked.

âI think weâve found the man who stole our amethystâat least we think we know where he is!â

âWhere?â Joe blurted.

Iola explained that she, Callie, and Chet had gone rock hounding again that morning in the hills outside Bayport. While they were trying to locate the spot where the girls had picked up the amethyst, they had glimpsed a man trailing them at a distance.

âDid he look like the fellow who questioned you at the gem shop?â Frank put in,

âHe was skulking too far behindâand ducking out of sight whenever we looked back,â Iola said, âso we couldnât be sure.â

âWhere are Chet and Callie?â Joe asked.

âThey stayed behind. We made a fire and now theyâre having lunchâacting as if nothingâs wrong. But Chet told me to sneak back to the car and get you two.â

âOkay. Hop in your jalopy and lead the way,â Frank said. âWeâll follow you.â

Iola drove into the hills west of Bayport. Frank and Joe stayed close behind in their convertible. Finally the jalopy pulled off the road. The Hardys parked nearby.

âWeâll have to do some walking,â Iola said.

A five-minute hike brought them to a hill overlooking a narrow ravine. Iola explained that Chet and Callie were waiting just beyond. âAnd the man whoâs been shadowing us is down there somewhere among all those rocks and shrubsâat least, he was when I left to get you.â

âA perfect setup,â Joe gloated. âFrank, suppose you and I go into the ravine at this end and flush him out? Then heâll either have to break for high ground or go right out past Chet.â

Frank agreed to the plan, and the boys wound their way down the hillside and up the floor of the ravine. Iola headed along the brow of the hill to rejoin Chet and Callie.

The Hardys spread out, searching among the brush and boulders. Twenty minutes later they emerged at the opposite end of the small canyon, their faces registering disappointment. Chet and the girls ran to meet them.

âDid you find him?â Chet asked.

Frank shook his head. âNo, but there are signs he was there.â

âWe spotted a trail of broken brush where someone climbed out of the ravine,â Joe added.

Chetâs moonface sagged. âRats! I thought sure we could nab him!â

âIâll bet he guessed that Iola went for help,â Callie put in, âso he decided heâd better not stay around.â

The Hardys drove home, eager to tackle their investigation of Aden Darrow. Mrs. Hardy informed them that Jack Wayne had telephoned from the airport. Frank called him back.

âStrang landed about an hour ago,â Jack reported. âI tried to reach you, but couldnât.â

âAnyone with him?â Frank inquired eagerly.

âJust the pilot, Al Hirff. That black sports car didnât show up, but another car did. A tough-looking guy met them and drove off with Strang.â

âWhat about Hirff?â

âStill here at the airport. I tried to strike up a conversation with him, but no luck.â

âGood work, Jack,â Frank said. âKeep trying.â

Frank passed the news to Joe. The boys ate a quick lunch of sandwiches and lemon pie, and then prepared to place a long-distance call to Western State University. Before they could do so, the telephone rang. Joe answered.

âThis is Mr. Filmer at the gem shop,â said the voice at the other end.

âOh, yes, Mr. Filmer. Is anything up?â

âWell, a man came into my shop a while ago with three stones that he wanted me to appraise. I donât know what sort of mystery you boys are working on, but I thought you might want to knowâthe stones were amethystslâ

CHAPTER IX

Secret Cruiser

JOEâS pulse quickened when he heard of this promising new lead. âWeâll be right over to talk to you, Mr. Filmer!â he exclaimed.

Hanging up, he told Frank what the gem-shop proprietor had said.

âMaybe weâre onto something,â Frank agreed.

Aunt Gertrude paused in the midst of trimming a pie crust as they rushed out through the kitchen door. âLand sakes! Where are you boys off to now?â she scolded. âDonât you realize youâll ruin your digestions?â

âOn your cooking? Why, Aunty!â Joe grinned and ducked out before she could retort.

The boys hopped into their convertible and drove to the shop on Bay Street. Although Mr. Filmer again looked somewhat nervous, and obviously had no desire to become involved in a criminal case, he seemed eager to be helpful.

âThis man who brought the stonesâhad you ever seen him before?â Frank inquired.

âNo, and he gave no name,â Mr. Filmer replied. âThe amethysts were uncut stonesâquite large.â

âGenuine?â

âOh, yes, indeed.â

âDid you ask where he got them?â Joe put in.

âWell, I tried to find out where they came from, but he was very evasive. And he wouldnât leave the stones for cutting and polishing, although I offered to do it very reasonably.â

âWhat did this fellow look like?â Frank asked.

âOh, he was big and husky.â The proprietorâs Adamâs apple bobbed as if the thought made him uneasy. âAnd he was dressed rather sportily. His hair was bushy and he had on a plaid sport coat.â

Frank darted a surprised glance at Joe. The description clicked!

âSounds like Duke Makin,â Joe muttered. Hoping for a further lead, he asked Mr. Filmer, âDid you see what kind of car he was driving?â

âI donât think he came in a car,â the proprietor replied, âalthough someone may have dropped him off, I suppose. But I watched when he left and I saw him get into a taxi at that stand across the street.â

âHow long ago was that?â Frank asked.

âMmm, say half an hour.â

âThanks, Mr. Filmer! Youâve been a big help!â

âDonât mention it, boys.â

Frank and Joe hurried across the street. A taxi driver was slouched in his taxi, reading a newspaper. The boys described Makin to him and asked the man if he had seen what cab driver had driven off with him.

âThat was Mike, I think. Should be back here soon, unless he picked up another fare.â

The Hardys returned to their convertible to wait. They fidgeted impatiently as twenty minutes went by. At last another taxi pulled into the stand. The first driver looked up from his paper, gave the boys a two-fingered whistle, and jerked his thumb toward the other taxi. Frank and Joe strode across the street and questioned the man who had just arrived.

âSure, I know the guy you mean,â he told them. âI took him out to some little picnic ground on Shore Road.â

âPicnic ground?â Joe echoed in surprise.

âYeah, it did seem like a funny place for him to get out,â the driver said. âI figured he probably planned to meet someone there.â

At Frankâs request, the driver described the spot and sketched a map. Frank tipped him, and the boys hurried back to their own car.

âLetâs take a look at the spot right now,â Joe proposed. âWe might pick up a clue.â

âRight!â Frank took the wheel and soon their convertible was rolling along Shore Road.

In a few minutes they came to the spot the driver had described, a small clearing laid out for picnickers. A family was eating at one of the tables. Otherwise, the site was deserted.

The Hardys got out to look around. Beyond the clearing, the ground was wooded and sloped steeply down to the shore of Barmet Bay.

âI wonder what Makin was doing around here,â Joe said.

âHe must have had some reason,â Frank said. âMaybe we can find it.â

The two boys wandered around the fringes of the picnic area, peering among the trees and shrubbery. Suddenly Joe gasped and pointed toward the water.

âLook, Frank!â

Far below, and about a hundred yards to seaward from the point of the bay at which they were standing, the shore was indented by a reedy inlet. A cabin cruiser lay anchored close to shore.

âOhâoh! Iâll bet thatâs the answer, all right,â Frank agreed. âMaybe itâs the same cruiser the frogman came from!â

The Hardys scrambled along the brow of the slope until they were overlooking the inlet. Even here the cruiser was not completely visible. Its hull was screened by heavy clumps of reed and rushes, and the boysâ view was further blocked by the thick growth cresting the slope.

âSure picked a good place to hide,â Joe muttered. âLetâs go down closer.â

The Hardys began picking their way cautiously down the steep hillside. But as the trees and brush thinned out, they themselves were exposed to view as they moved close to the cruiser. Suddenly they saw a man emerge from the cabin and cock one arm.

âLook out!â Frank cried out. âThat may be a bomb heâs throwing!â

The boys flattened themselves in the underbrush as an object spun through the air.... Whoosh!

âA gas grenade!â Joe yelled to his brother. The boys sprang to their feet and hurried back up the slope as the throb of a boat engine reached their ears. In seconds the hillside was filled with billowing purple smoke!

Gasping, choking, and with tears streaming from their eyes, Frank and Joe finally reached the top of the hill and ran toward the picnic ground. The family at the table stared at them in wide-eyed excitement.

âWhatâs happening?â the man shouted.

âSome prankster in a boat down there threw a tear-gas grenade,â Frank said, so as not to alarm the group.

âWhy, thatâs terrible! Someone should call the police!â the manâs wife said.

âWeâll report it,â Frank promised.

Fortunately, an offshore breeze was blowing the smoke away from the picnic ground and out onto the bay. But the smoke screen hid the cruiser completely from view.

The Hardys hurried to their car and warmed up the short-wave set. Frank contacted the Coast Guard station and the radio operator on duty promised that an effort would be made to spot the cabin cruiser. There seemed little hope of identifying it, however, among all the other craft on the bay, especially since the boys had noticed no special features, not even the cruiserâs name.

Frank and Joe were glum as they drove home. âDo you suppose Makin was aboard?â Joe asked.

Frank shrugged and frowned uncertainly. âI donât know. That inlet was practically a swampâit sure didnât look like an easy place to get on or off the cruiser. But the purple smoke was the same kind we ran into the other night. That would seem to link the cruiser itself to Strang.â

Joe glanced at his brother. âIncidentally, why did you ask Mr. Filmer if those amethysts were genuine?â

âMakinâs a confidence man plus his other racketsâremember? I thought he might be planning to use the stones for some con game.â

As soon as the brothers arrived home, Frank placed a call to Western State University. He explained that he wanted information about a former professor named Aden Darrow.

âIâll connect you with Dean Gibbs,â the switchboard operator replied.

Frank identified himself to the dean.

âOh, yes. Iâve often heard of your father,â Gibbs said. âWhat can I do for you?â

Frank explained that Darrowâs name had come up in connection with a case the Hardys were investigating. He asked if the dean could tell him anything about Darrowâs background.

âUp until last term, Professor Darrow taught a special course in crime-detection methods here,â Dean Gibbs replied. âHe has a background in both physical and organic chemistry. Before he joined our faculty, he worked in police crime labs in several western cities.â

âWhy did he leave the university?â

âWell, that was rather unfortunate,â Gibbs said. âYou see, he had been trying to raise funds for research on a project which he claimed would be of great value to the police.â

âWhat sort of project?â Frank inquired.

âTo be honest, we know very little about it. Professor Darrow had become secretive and suspicious. In fact, we felt he was on the verge of a nervous breakdown. After the school refused to allot any money for his project, Darrow became extremely upset and resigned.â

âI see.â Frank was thoughtful for a moment, then said, âWe were told he recently bought a house here in Bayport. Did he say what his plans were when he left the university?â

âNo, not a word. In fact, we had no idea of his present whereabouts before you called.â

Frank was just hanging up when a plane roared low over the house. The boys could hear it turn and zoom back as if it were buzzing the Hardy residence.

âThat may be Jack Wayne!â Joe exclaimed. He rushed to look out a window. âItâs Skyhappy Sal, all right. Maybe Jack wants to talk to us!â

The boys dashed downstairs and switched on their two-way radio. Joe took the microphone.

âHardys to Sal.... Can you read us?â

The pilotâs voice crackled over the speaker, âLoud and clear, Joe! Listen, I think Iâve picked up a hot lead from Hirff. It may tie in with those jewel robberies your dad isââ

Jackâs voice was drowned by a sudden burst of static. When it came through again, it was so faint the Hardys could catch only a few words:

âIf the tigers bite ... amethyst ...â

There was another burst of static. The radio message died out completely!

CHAPTER X

The Ghostly Figure

JOE tuned the receiver anxiously, trying to restore a clear signal.

âHardys to Sal! Come in, please! ... Hardys calling Sal!â

There was no response. The two boys looked at each other, worried and mystified.

âWhat do you suppose went wrong with the transmission, Joe?â his brother muttered.

âSearch me. What Iâm wondering is whether Jackâs okay!â

The brothers ran up the basement stairs and dashed outdoors. Shading their eyes, they scanned the sky. Jackâs plane was now a mere speck in the blue, rapidly dwindling from sight. It was heading on a southerly course.

âAt least heâs still up there!â Frank said, half under his breath.

Joe added, âLetâs hope he makes it all the wayâwherever it is heâs going!â

The boys went indoors and tried for a while longer to re-establish radio contact with Skyhappy Sal, but their efforts were unsuccessful. Frank and Joe returned to the living room and slumped into comfortable chairs.

âIâd sure like to know what Jack was trying to tell us,â Frank brooded.

âSo would I. That message was weird!â Joe furrowed his brow, trying to make sense out of the few words that had filtered through. âIf the tigers bite ... What could he possibly have been referring to, Frank?â

âDonât ask me. Itâs strictly Greek as far as Iâm concerned.â Frank scowled in deep thought. ââTigersâ might refer to animals in some zoo, I suppose. Or maybe to tigers being brought into the country by some animal importer.â

Joe shook his head. âSounds pretty farfetched. Jack was flying south. That might mean he was heading for the Caribbean area.â

âMaybe. So what?â

âWell, they have jaguars down in Central America. And, in Spanish, the jaguar is called tigre.â

âFor that matter, what about tiger sharks?â Frank broke off abruptly and sprang up from his chair. âWait a minute! We must be getting daffy with the heat. We can find out where Jackâs going just by checking with the airport tower!â

Frank strode to the telephone in the front hall and dialed. He talked for a few moments, then hung up and returned to the living room, wearing a frustrated expression.

âThe tower operator says Jack didnât file a flight planâwhich probably means heâs just making a brief local flight.â

âThen we should be hearing from him soon,â Joe suggested.

âWe hope!â Frank added, crossing his fingers.

Just then a car pulled up in front of the house with a squeal of tires and a series of loud backfires.

âDonât tell meâlet me guess. Itâs Chet Morton,â said Frank.

Joe grinned and glanced out a window at Chetâs red jalopy. âWho else?â He went to open the front door as their chunky friend came bounding up the walk. âHi, Hercules! Howâd you make out on the amethyst trail?â Joe asked.

âWe didnât.â Chet went on into the living room and flopped onto the sofa. âThose girls still canât remember where they picked up the stoneâand we didnât find any new ones, either.â

âTough luck,â Frank sympathized.

The Hardys gave Chet news of the latest developments, including Jack Wayneâs radio message.

âTigers?â Chetâs eyes bulged. âI hope youâre not going to be bumping into any of those on this case!â He paused to sniff the aroma wafting from the kitchen. âMmm! Do I smell chicken?â

âFried chicken.â Mrs. Hardy had paused at the door and smiled as she glanced in. âAnd thereâll be honey to go with Aunt Gertrudeâs hot biscuits. Would you like to have dinner with us, Chet?â

âWould I? Boy, and how! But Iâd better call Mom and let her know.â

An hour later, the meal just over, the doorbell rang. Frank went to answer it.

âTelegram for Frank and Joe Hardy,â said a messenger.

Frank signed for it and ripped open the yellow envelope as he brought it into the living room.

âHey! Itâs from Dean Gibbs at Western State University!â He read the telegram aloud:

PROFESSOR DARROWâS SISTER EAGER TO FIND HIM. IF POSSIBLE PLEASE CONTACT PROFESSOR. ASK HIM TO CALL HER.

âWow! What a break!â Joe exploded.

Chet looked puzzled. âHow do you figure that?â

âThis gives us a perfect excuse to go right up to the Perth mansion and find out whatâs going on!â Frank explained. âWant to come along?â

âWell, I dunno.â Chet squirmed uncomfortably. âMaybe youâd better count me out.â

âDonât be chicken. Youâre coming with us!â Joe said, slapping the plump youth on the back.

Frank said, âI just thought of something. If Professor Darrow taught crime-detection methods, maybe we can find some articles by him in Dadâs journals. Thatâll give us material to work up a conversation with him. It might even furnish us a clue to his research project!â

âGood idea!â Joe agreed enthusiastically.

In their fatherâs study the Hardys checked the annual index of each of the three criminology journals to which their father subscribed. They could find only one article authored by Aden Darrow. It dealt with new data on the power of light beams.

Although the article gave no hint of Darrowâs present field of research, it did include a photograph of the professor demonstrating some ultraviolet equipment. He wore eyeglasses and was bald, with a rumpled fringe of gray hair.

âWell, at least we know what he looks like,â Joe remarked.

The boys hurried to the Hardysâ convertible. A red glow of sunset suffused the western sky as they drove out of Bayportâs residential district and into the wooded outskirts of town. Soon they pulled up on the dirt lane directly in front of the Perth mansion.

âYou fellows handle it,â Chet said. âIâll stay in the car.â

Grinning, Frank and Joe walked up the tree-covered slope to the house. Joe pressed the doorbell. Moments passed. He was about to ring again when the door suddenly opened. A tall, dark-haired, hatched-faced man confronted them.

Noel Strang!

âWell, what do you want?â he demanded, giving the boys a hard stare.

âWe have a message for the man who lives here,â Frank said boldly.

âI live here,â Strang retorted. âWhat is it?â

âWe mean Professor Aden Darrow,â Frank said, displaying the telegram.

Strang reached out to take it, but Frank made no effort to give him the paper. âSorry, but the message is personal. Itâs from his sister.â

âToo bad!â Strang snapped. âProfessor Darrow suffered a breakdown from overwork and had to leave on a long vacation. I have no idea how to reach him.â

âDid he go out of the country?â Joe spoke up. âIf so, maybe we couldââ

The door slammed in the boysâ faces!

Frank and Joe looked at each other uncertainly then turned and started down the veranda steps. In the gathering dusk a light suddenly blazed on in an upstairs window. Joe glanced up over his shoulder, then clutched Frankâs arm.

âLook!â he exclaimed.

Through the window curtain, they glimpsed a man who seemed to resemble Professor Darrow! An instant later he moved out of sight.

âStrangâs probably watching us,â Frank muttered. âLetâs go!â

At the car they discussed their next move.

âLetâs drive around till it gets dark, and then come back and keep watch on that window,â Joe suggested.

âOkay,â Frank agreed.

Leaving the dirt lane, the boys cruised back and forth along the main road until darkness had closed in. Then they returned and parked their convertible well out of range of the house. Taking flashlights, the boys started up the slope. Chet was not enthusiastic but agreed to accompany them.

Suddenly Frank paused as moonlight glinted off something on the ground. He switched on his flashlight cautiously, covering the lens with his fingers to shade the glow.

There lay the square tiled surface Chet had described to them! The dragon design was formed in colored mosaic.

âThatâs it!â Chet whispered excitedly.

âHow come we couldnât find it before?â Joe said.

âMaybe sometimes itâs covered over with brush and loose shrubberyâon purpose,â Frank reasoned.

Before they could examine the spot more closely, Chet gasped and pointed off to the left. A white figure was moving slowly among the trees!

âItâs that spook again!â Joe exclaimed. âThis time, letâs nail him!â

Chet moved his lips in speechless terror, but rather than be left behind, he went lumbering off after the two Hardys.

Frank and Joe sprinted straight toward the ghostly figure, determined not to let it elude them a second time. But the phantom had already seen them and went darting off like a vanishing wisp of mist.

The pursuit circled and zigzagged about the mansion grounds. Chet soon lost all fear as he became convinced that the fleeing specter was only flesh and blood. He joined in the chase with zest, his sturdy legs pumping as if he were pursuing a rival teamâs ballcarrier on the Bayport High football field.

Frank was in the lead, with the other two boys on either side searching swiftly among the trees.

âJoe! Can you see him?â Frank called back. âI think he went that way!â

There was no answer. Frank glanced over his shoulder, then gasped.

Joe had disappeared!

CHAPTER XI

A Parcel of Gems

FRANK skidded to a halt and peered intently through the darkness. âJoelâ he called in almost a whisper. âJoe! Where are you?â

Chet hurried to Frankâs side. âWhatâs wrong?â he asked anxiously.

âI donât know. Joe was only a few yards from me just a minute ago. Now I canât see him.â

Chet glanced around. The white phantom had also disappearedâswallowed up in the gloom.

Suddenly Joeâs muffled voice reached their ears. âThis way, you guys! But watch your step! I fell down a hole!â

Frank and Chet hurried toward the sound, with Frank beaming his flashlight over the ground in front of them. Both boys stopped as the yellow glow revealed a large, square hole.

âHey! Thereâs that tiled thing!â Chet exclaimed. âBut itâs open!â

Frank saw that the whole tiled surface had flapped downward. It was now hanging flush against one side of the hole, its colored mosaic glistening in his light.

âIâm down here,â called Joe. âThat tiled square must be hinged like a trap door. Either its supports gave way, or someone mustâve opened it by remote control. And thatâs not allâthereâs a tunnel down here!â

Frank shone his flashlight down the hole. It was brick-walled and about twelve feet deep. In the side opposite the flap-down tiled surface was an opening just large enough for Joe to enter without stooping. Alongside this opening, a metal ladder was attached to the wall, for climbing in or out of the hole.

âWow!â Chet dropped to his knees and peered below. âWhere do you suppose that opening leads?â

âIâll bet thereâs a tunnel going all the way to the house,â Joe answered, shining his own beam through the opening.

Frank told Chet of Mrs. Hardyâs theory that the tiled surface had been the floor of an old summerhouse. He added, âThe summerhouse was probably built on purpose to hide this end of the tunnel.â

âThatâs quite a drop,â Frank said anxiously. âAre you hurt, Joe?â

âNo! I managed to break the fall. It was easy after some of those judo slams weâve takent Besides, this floor feels spongy. It must have been padded in case of an accident.â

Frank peered in all directions. âLooks as though weâve lost our spook for good.â

âThen letâs search this tunnel,â Joe proposed.

Chet gulped uneasily. âHow do you know what weâll find at the other end?â

âWe donât. Thatâs why we want to find out.â

âB-b-but you said yourself that someone may have opened this by remote control,â Chet said shakily. âHow do we know the crooks arenât using the tunnel right now? Andâand they may even be trying to lure us into a trap!â

Joe chuckled and aimed his flashlight into the tunnel entrance. âThereâs some kind of phone in there, hanging on a hookâprobably an intercom to the house. Want me to call and ask?â

Frank looked serious. âI think Chet has a point, Joe. Maybe one of us should stay hereâoutside the tunnelâin case of emergency.â

âOkay, you two flip a coin. Me for the tunnel!â

Frank spun a nickel, caught it, and slapped the coin on the back of his other hand. âWinner goes with Joe. You name it, Chet.â

âUhâwellâheads.â

Frank shone his beam on the coin. âHeads. Guess youâre elected, Chet. But lookâyou donât have to go! Why donât you stay here and Iâllââ

âNothing doing,â Chet protested bravely. âI won the toss, so Iâll go.â With the look of a condemned man en route to the electric chair, the pudgy youth climbed down the metal ladder. He could smell the dank, musty passageway.

Joe was already inside the tunnel entrance. âCome on!â he called back over his shoulder.

As Chet followed Joe into the tunnel, his bulky form brushed the intercom phone off its hook. Instantly a red light flashed on, evidently a signal to indicate that the circuit was now âliveââno doubt a buzzer was ringing at the other end of the line!

Chet clutched Joe. They stared at the unit as if it were a rattlesnake about to strike.

Suddenly a voice crackled from the phone. âHello ... hello!â Joe snatched up the instrument as the voice went on, âIs that you, Waxie?â

Joe responded in a curt, flat tone, âYeah?â

âWell, what do you want now?â the voice inquired irritably. âWhat did you come back for?â

Joe glanced helplessly at Chet; then, snatching at the first inspiration that came into his head, he replied nasally, âOrders.â

âOrders? Whatâs the matter with you, Waxie? You gettinâ absent-minded? The boss gave you all the dopeâabout the disappearing floorââ The voice broke off as if the speaker had suddenly become suspicious. âWait a minute! Whatâs going on out there? Who is this?â

Joe dropped the phone and gave Chet a shove. âCome on! Letâs go!â he muttered urgently. âNow weâve really stirred up a hornetâs nest!â

The boys scrambled up the ladder and told Frank what had happened. All three ran for the car. In moments Frank was gunning the motor and the convertible was roaring off down the lane.

âWhat a bad break!â Joe grumbled as they turned onto the main road.

âIt was my fault,â Chet admitted, âand Iâm sorry. But I sure learned somethingânamely, not to get mixed up in any more of your nutty cases! So next time count me out!â

The Hardys chuckled and Joe apologized for his remark. Between them, the two young sleuths managed to make Chet change his mind by telling him they could not get along without him.

The mantel clock in the living room was just chiming nine when Frank and Joe arrived home. A note propped on the dining-room table explained that their mother and Aunt Gertrude had gone to visit a neighbor down the street.

The boys got apples and milk from the refrigerator. Frank poured two glasses and they sat down in the kitchen to discuss their case.

âThink we should notify the police?â Joe said.

âAbout Darrow?â Frank shrugged uneasily. âI donât know. Weâre not sure it was he that we saw. For all we know, he may have told Strang not to admit any visitors. Remember, Dean Gibbs said he had become very huffy.â

Joe nodded. âI sure wish Dad or Sam Radley were here to advise us.â

A moment later the radio signal buzzer sounded from the basement. âMaybe thatâs Dad now!â Joe exclaimed, setting down his glass and tossing his apple core into the garbage can.

The boys rushed downstairs and soon established radio contact with their father, who was calling from Chicago.

âSam and I are still sifting leads here,â Fenton Hardy reported. âThe thieves seem to have covered their tracks pretty well. Incidentally, the same method was used as on all the other jobs. The private patrolman guarding the place blacked out and has no recollection of what happened.â

The detective listened as Frank and Joe brought him up to date on events in Bayport. He, too, was baffled by Jack Wayneâs interrupted radio message. When the boys asked what to do about the situation at the Perth mansion, he was silent for a moment, then said:

âThat window at which you think you saw Darrowâwas it barred or heavily screened in any way?â

âNo, it was partly open,â Joe replied.

âThen if the man was Darrow, it hardly sounds as if heâs being held against his will. Strang undoubtedly has some kind of undercover setup there at the mansion. Darrow may not be aware of it. And we still have no proof Strangâs involved in these jewel thefts. Proof is what we need before we move in on him. Meantime, I have another job for you boys.â

Mr. Hardy explained that he had just received another anonymous phone tip. âThe caller simply said âGo to Haley BuildingâBayportâ and then hung up. Sounds to me like another fake lead, but I wish you boys would check it.â

âWeâll do it right away, Dad,â Frank promised.

Two minutes later the brothersâ convertible was speeding downtown. It pulled up in front of a new office building on Main Street.

An elderly night watchman was seated at a desk in the lobby. As Frank and Joe entered, he glanced up at the wall clock, which read 9:41.

âKind oâ late, you fellers. This placeâll be closinâ up in about twenty minutesâin fact, the buildingâs practically empty now. Someone you wanted to see?â

When Frank showed his identification, the watchmanâs face brightened. âOh, Fenton Hardyâs boys, eh? Well, Iâm pleased to meet you!â

Frank told why they had come and asked if anything unusual or suspicious had happened that evening. The watchman shook his head.

âNo. Except a parcel oâ gems was delivered to Paul Tiffman up on the fifth floor âround eight-thirty. But I knew beforehand that was cominâ. Tiffmanâs a diamond merchant, yâsee. When he stays late like tonight to receive a delivery, he always tells me. Most nights, everyoneâs gone by six.â

Both Frank and Joe had stiffened at the mention of gems. Before they could comment, the elevator signal rang. The watchman rose.

â âScuse me, boys. I have to double as elevator operator after six oâclock. That must be Tiffman now, wantinâ to go home.â

The Hardys asked to ride up. When the watchman opened the elevator door on five, they saw a worried-looking man, plump and dark-mustached. âHasnât that messenger arrived yet?â he asked.

The watchman looked surprised. âWhy sure, Mr. Tiffman. He was here at eight-thirty. I took him up, and then brought him down again later after he delivered those gems to you.â

Tiffmanâs jaw dropped open. âAre you crazy?â he spluttered. âI havenât received any gems. No one has come to my office this evening!â

CHAPTER XII

The âSeacatâ Clue

THE watchman stared at the diamond merchant. Both their faces were turning an angry crimson.

âMr. Tiffman, I donât know what kind of a joke youâre playinâ,â the watchman said, âbut I saw that messenger with my own eyes!â

âAnd I donât know, Mike, what kind of a joke youâre playing!â Tiffman roared back. âI tell you no messenger came to my office!â

âCanât help that! He came here and left!â

âI think youâd better call the police at once,â Frank put in quietly.

âWho are you?â Tiffman snapped.

âWeâre sons of Fenton Hardy, the private detec tive.â Frank explained about the anonymous phone tip. Tiffmanâs attitude promptly changed.

The watchman called the police. A prowl car was at the building within moments, and Chief Collig arrived a few minutes later, accompanied by a plain-clothes detective.

âYou boys watch the door,â Collig told the two prowl car officers. âThe rest of you come upstairs to Mr. Tiffmanâs office.â

The five crowded into the elevator and rode up. Tiffmanâs office door was flush-paneled with a pane in one corner. It was marked â507â in modernistic metal numbers, and the name plate below said: PAUL TIFFMAN, Gemologist.

After the Hardys had told Collig about the anonymous tip-off and the two men had told their stories, the police chief commented, âSounds to me as if that messenger pulled a fast one.â

âYou mean he simply walked off without delivering the gems?â When Collig nodded, Tiffman frowned and shook his head. âThat doesnât make sense. If he were planning to flee with the diamonds, why bother coming to Bayport at all?â

âIs there any chance he could have been waylaid between the elevator and this office?â Joe put in. âIf so, the thug might have dragged his body somewhere out of sight, and then gone down in the elevator posing as the messenger.â

Collig turned to Mike. âHow about it? You sure the man you took down was the same man you brought up here?â

âSure was,â the watchman said tartly, âunless he was awful good at disguises. That messenger had red hair, freckles, and a wart on his cheek. So did the man who rode down.â

âHave you ever seen this messenger?â Collig asked Tiffman.

âWouldnât know him from Adam.â

âWho sent him?â

Tiffman named a firm of diamond importers in New York City.

âEver had deliveries from them before?â

Once again Tiffman shook his head. âNormally I make buying trips to New York once a month and select my gems right there,â he explained. âBut it happens I want to show a special selection to a wealthy client out in Dorset Hills tomorrow. The New York firm was expecting a new shipment from South Africa today, so they promised to make up a parcel and rush it down here tonight.â

âHow was the messenger traveling?â Collig inquired.

âBy trainâat least they told me heâd get in on the eight-fifteen.â

Collig picked up the phone and called New York City Police Headquarters and asked them to watch the incoming trains. He also called Bayport Headquarters and told his desk sergeant to put out a statewide alarm for the messenger. Finally he tried to contact the diamond importers, but evidently their office was closed for the night.

âWell, thatâs about all we can do now,â Collig said, hanging up. âBut weâll have that messenger here with some answers tomorrow morning or my nameâs not Clint Collig!â

Frank and Joe hurried home, intending to radio their father immediately and report the mystery. But their mother, who had returned with Aunt Gertrude, told them he could not be reached.

âYour father called while you boys were gone,â she explained. âHe and Sam Radley had to rush down to Gary, Indiana, to follow up some urgent clue, and they probably wonât get back to Chicago before tomorrow afternoon.â

Next morning, the Hardys still had no further word from Jack Wayne, so they drove to the airport to make inquiries about him. At the office of the Ace Air Service, they found a young freelance pilot named Tom Lester, who often handled charter flying assignments for Jack.

âAre you boys looking for Jack, too?â he asked.

âWe sure are,â Frank replied. He told Tom about the puzzling interrupted radio message.

Tom could offer no explanation. âIt certainly sounds strange. What worries me is that Jack filed no flight plan. Ordinarily, under those circumstances, I would have expected him to be back last night.â

âDo you think he may have crashed?â Frank inquired anxiously.

âItâs possibleâespecially if his radio conked out. That would explain why he hasnât called for help.â Tom rubbed his jaw thoughtfully. âI donât suppose you boys feel like telling me any more about this case youâre working on?â

Knowing the young pilot could be trusted, the Hardys filled him in on the mystery. Tom Lesterâs keen blue eyes showed interest at once.

âSounds to me as if Jackâs onto something big,â Tom surmised. âMaybe he even managed to worm himself into Hirffâs confidence. If he went to meet some of the gang, maybe he just hasnât had a chance to contact you again.â

âThat makes sense, all right,â Joe said.

âHe didnât leave any message for you on his desk?â Frank asked Lester.

The pilot shook his head. âI didnât notice anything. Letâs take another look.â

Almost at once Frank pounced on Jack Wayneâs phone pad. âLook at this!â he exclaimed.

The pad bore a scribbled notation in Jackâs handwriting: Amethyst calling Seacat.

Tom read the message with a frown. âThat word âamethystâ ties in with his radio call!â

âDo you know this guy Al Hirff?â Frank asked.

âI know of him, and Iâve seen him,â Lester replied, âbut Iâve never met him.â

âLetâs look for him,â Frank suggested. âIf we could work him into a casual conversation, we might fish out a clue.â

The private rented hangar in which Al Hirff kept his own plane was locked. The Hardys and Tom Lester wandered around the airport, looking into other hangars and the passenger terminal, but could not find Hirff. When Frank and Joe finally left, Tom promised to keep his eyes open for the pilot.

From the airport, the boys drove straight to Bayport Police Headquarters for news on the previous nightâs diamond mystery. On the way they discussed the curious notation on Jackâs phone pad.

âThat word âSeacatâ sounds to me like the name of a boat,â Joe speculated.

Frank agreed. âYou know, Joe, it might even be the name of that mystery cabin cruiser!â

At headquarters the desk sergeant told them to go on into Chief Colligâs office. A red-haired man, freckled, and with a wart on one cheek, was seated in front of the chiefâs desk.

âGlad youâre here, boys,â Collig told them. âThis is Dan OâBannion, the messenger.â

The Hardys listened to OâBannionâs story.

âLike I told Chief Collig,â the messenger said, âI took that parcel of gems straight up to Tiffmanâs office. I delivered them to him and went right back to New York on the next train.â

âDid you get a receipt?â Frank asked.

âYou bet I did! Itâs on the chiefs desk.â

Collig held up an official receipt form. It was signed âPaul Tiffman.â

âIâve called Tiffman and asked him to come over here,â Collig added.

When the diamond merchant arrived, OâBannion looked astonished. âThis isnât the man I gave the gems to!â he exclaimed.

âAnd Iâve never seen you before, either,â Tiffman said tartly.

âYou certainly werenât in the office when I arrived,â the messenger agreed.

âI was in my office every minute of the evening. And nobody could have taken my place!â

Tiffman added that the signature on the receipt form was not his, and proved it by displaying his driverâs license and other identification cards. OâBannion shrugged, tight-lipped.

Frank suggested they all go to the Haley Building. âIf we reconstruct what happened last night, it may throw a new light on the mystery.â

âGood idea, Frank!â Chief Collig said.

In ten minutes they were on their way to Tiffmanâs office. As they stepped off the elevator, the messengerâs expression changed.

âWhatâs the matter?â Joe asked him.

OâBannion pointed to a large, unsightly crack in the wall plaster. âIâm positive that crack wasnât there last night,â he said.

âItâs been there for the past two weeks,â Tiffman said. âSome careless workmen banged into the wall when they were delivering furniture.â

When they entered Tiffmanâs office, OâBannion looked more bewildered. âThis wasnât the office I came to!â he exclaimed. âThe furnishings were altogether different!â

âMaybe you need glasses!â Collig snapped. âDidnât you look at the sign on the door?â

âI did look!â OâBannion flared back. âThe office number was 507 and the sign said, âPaul Tiffman, Gemologistâ!â

Chief Colligâs face took on a tinge of purple. âIâm sending for the county polygraph expert!â he roared, thumping his fist on the desk. âYou and Mr. Tiffman and the night watchman are all going to get lie-detector tests!â

âThat suits me fine!â OâBannion snapped.

Frank and Joe were mystified as they drove away from the Haley Building. Both boys would have liked to go out in their boat to sift through their thoughts in the fresh salt air and sunshine. Since the Sleuth was not yet repaired, they settled for a drive to the harbor.

The Napoli was moored at the dock. Tony was touching up worn spots with varnish, while Chet Morton lolled on a thwart, practicing knots. Frank and Joe strolled out to chat with them.

âAnything new on the case?â Tony asked.

âPlenty,â Joe grumbled. âThe problem is how to unravel it all.â

âRats!â Chet muttered. âI just canât seem to tie a bowline on a bight!â

Suddenly Frank let out a gasp. âMaybe thatâs what Jack Wayneâs message meant!â

CHAPTER XIII

Snoop Camera

JOE gave his brother a puzzled look, at first seeing no connection between Chetâs remark and Jack Wayneâs interrupted radio message.

âWhat do you mean, Frank?â

âLook! Weâve been assuming all along that when Jack said âtigersâ biteâ he meant the kind of biting thatâs done with teeth,â Frank observed.

Joe exclaimed, âI get it! You think he was talking about the kind of bight spelled b-i-g-h-t!â

âExactly.â

âYou mean the message had something to do with a rope or line?â Chet asked blankly.

Frank shook his head. âThat wouldnât make much sense. But remember, âbightâ can also mean a sort of bay or indentation in a coastline. In other words, maybe Tigersâ Bight is the name of a place.â

Joe snapped his fingers excitedly. âSure! Tigersâ Bight could be the name of the place Jack was heading when we saw him fly south!â

âAny of you fellows ever hear that name before?â Frank asked.

Chet shrugged his beefy shoulders. âNot me.â

Joe also had to admit that the name was new to him. But Tony frowned thoughtfully. âThat rings a bell. I have a hunch I have heard it.â

âWhere?â the Hardys asked in chorus.

âI donât know. But if youâre right, it must be some place along the coast. Maybe Iâve been there in the Napoli. Why donât we look on a map?â

Tony opened his boat locker and took out a sailing chart of the Barmet Bay area. He and Chet then climbed up onto the dock, and the boys spread out the chart. But after poring over it for several minutes, they could find no such name as Tigersâ Bight.

âAnother clue conked out!â Joe muttered.

âLetâs not give up too soon,â Frank said. âMaybe itâs not important enough to show on the mapâor maybe the nameâs not official.â

âWhy donât you ask old Clams Dagget?â Chet suggested.

âThatâs an idea,â Joe said. âHeâd certainly know if anyone would.â

Dagget was a retired seafaring man, who now operated a ferry service to Rocky Isle in Barmet Bay.

Frank glanced at his wristwatch. âClams wonât be here to pick up any more passengers before one-thirty. Letâs go home and have lunch, Joe. We can stop by later and ask him.â

âOkay. I can sure use some chow!â

Each of the boys ate two hamburgers and a generous portion of French fried potatoes. They were just finishing helpings of Aunt Gertrudeâs old-fashioned strawberry shortcake when the telephone rang. Tom Lester was calling from the airport.

âAl Hirff just showed up,â the pilot told Frank. âIf you want to talk to him, nowâs your chance.â

âWhere can we find him?â

âRight now heâs in the hangar, checking his plane. He has a pug nose and wears his hair in long sideburns. You canât miss him.â

âOkay. Thanks, Tom.â Frank hung up and told Joe. âItâs not one oâclock yet. Letâs whip out to the airport before we see Clams Dagget.â

âSuits me. And say, why donât I take my new camera along and snap Hirffâs picture? Dad might recognize him.â

âGood idea.â

Joe had recently bought an ultraminiature camera from money he had saved. It could be attached to his lapel for taking secret photographs. Both boys slipped on sport jackets to allay suspicions on Joeâs maneuver.

A short time later they pulled into the airport parking lot and headed for Hirffâs hangar. The door was open, and inside they could see a big, twin-engined amphibian plane. But the pilot was not in sight.

The boys walked cautiously into the hangar to look around for him. Joe shot an inquisitive glance at the airplaneâs cabin, but the fuselage was too high for a full inside view. He climbed up and noticed a folded navigation chart, with penciled markings, clipped above the pilotâs seat.

âHey, Frank!â Joe exclaimed excitedly. âI see a chart of the Bayport coastal areaâand it has some markings on it!â

Frank warned, âWatch it, Joe! Here he comes now!â A man who answered Tom Lesterâs description of Hirff was striding toward the hangar!

Joe quickly unhooked his lapel camera, held it up, and snapped a picture of the map. Then he jumped down.

âWhatâre you punks doing here?â the pilot yelled, charging into the hangar almost at a run.

Joe calmly snapped Hirffâs picture, then slipped the camera into the sport-coat pocket. The pilot, livid with rage, tried to hurl Frank aside and get at Joe.

Instead, Frank met the attack. He spun him around with a judo grip and followed with a punch to the jaw that landed the man on the floor. Hirff sat up and blinked in surprise.

Frank repressed a grin. âIf you want me to step out of the way, just ask politely.â

Hirff got to his feet, scowling. âAll right, wise guys! Suppose I call the cops!â

âGo ahead,â Frank said coolly. âThe hangar was open so we walked in to say hello. Didnât touch a thing.â

âWhen the police get here,â Joe added, âmaybe we can chat about Tigersâ Bight.â

The remark was a shot in the dark. Joe had hoped it might startle Hirff or provoke some interesting reaction. But the effect was out of all proportion to what Joe had expected. Hirffâs face paled and all the bluster seemed to go out of him.

âI ... I d-donât know what youâre talking about,â Hirff faltered. âSorry if I lost my temper. Thought maybe you kids had sneaked in here to strip the plane or something. Go on now, scram, and weâll forget all about it!â

âSure, if thatâs the way you want it.â Frank turned to his brother. âCome on,â he said.

Joe could not resist a parting taunt. âIf you change your mind about calling the police,â he needled, âthey can find us at the boat dock.â

Both boys could feel Al Hirffâs eyes burning into their backs as they walked toward the parking lot. Driving away, Frank remarked, âBoy! You sure struck gold that time ! But I hope it wasnât a mistake, telling him our next move.â

Joe shrugged. âI doubt if the gang would try any dirty work in broad daylight. Anyhow, if they do, so much the better. Thatâs one way to draw â em into the open!â

Frank met the manâs attack

At the boat dock a few passengers had already boarded the Sandpiper. But Clams Dagget was leaning against a bollard, smoking his corncob pipe, apparently in no hurry to shove off. He greeted the Hardys with a nod. âHi, lads! Howâs the detective business?â

âBooming,â Frank replied with a smile. âMaybe you can help us. Ever hear of a place called Tigersâ Bight?â

âSure. Down south of the bay. I once lost an anchor there.â

The Hardys became excited.

âWe couldnât find it on the map,â Joe said.

âAinât surprised,â Clams said, without taking the pipe out of his mouth. âThatâs just a nickname. âBout ten years ago there was a couplâ attacks on swimmers by tiger sharks that come in the bight, so folks thereabouts took to callinâ it Tigersâ Bight. No one goes there much any more. Pretty desolate now.â

Frank took out a pencil and a scrap of paper, and asked Dagget to draw a map so he and Joe could find the place. The old ferryman obliged.

The Hardys thanked him and started back to their convertible, which they had parked in a vacant lot on the opposite side of the road. As the two boys passed a roadside stand facing the road, Joe let out a startled yelp.

âFrank! Look!â Their car door was open and a man was pawing through the glove compartment!

Frank and Joe started to dart across the road but had to pause for a break in traffic. The man glanced around warily, saw them, and immediately fled through the lot. By the time the Hardys crossed the road, he was leaping into a waiting sedan. It sped off with a roar.

âLetâs go!â Frank shouted, rushing toward the convertible. He slid behind the wheel and Joe slipped in beside him. Frank whirled the car around, sent it bumping and bouncing across the lot, then shot out onto the road.

The chase continued for over a mile, with the sedan clearly in view. Then the Hardys saw it turn off to the right.

Moments later, the convertible reached the same spot and Frank swung the wheel. The car took the turn with a screech of rubber. They were now in a winding dirt lane with woods on both sides, and the sedan was out of sight.

Bang! The convertible suddenly spun out of control. Frank jammed on the brakes, seesawed the wheel, and managed to bring it to a lurching stop just before it crashed into some trees.

âWhew!â Joe let out a gasp of relief.

Somewhat pale and shaken, the boys climbed out to survey the damage.

âLeft front tireâs flat,â Frank announced.

âAnd thereâs what did it.â Joe pointed to a wicked-looking array of tacks, bent nails, and broken glass scattered across the lane. âThose crooks mustâve tossed the stuff out of their car before we turned into the lane.â

Disgusted, the Hardys got a jack out of their trunk and set about changing the flat tire.

Suddenly a small object flew spinning from the trees across the lane. It landed near the convertible and sent up a gush of purple smoke!

Frank stiffened in anger. âLook out, Joe!â he warned. âWeâre being attacked!â

Three men wearing gas masks had burst out of the woods and were charging toward the boys!

CHAPTER XIV

Tigersâ Lair

As THE smoke bomb burst and Frank yelled his warning, Joe was getting the spare out of the trunk, his back turned to the lane.

Joe whirled at Frankâs cry and saw the gas-masked men only a few yards away. He struggled to hoist out the spare wheel and hurl it at them, but two of the thugs pounced on him.

Frank rushed to his brotherâs assistance, clutching the lug wrench. The third man grabbed his arm, twisted the wrench away from him, and knocked Frank sprawling in the ditch.

In moments, purple smoke blanketed the area. The Hardys gasped and their eyes watered.

Joeâs assailants overpowered and searched him, one yanking the lapel camera from his pocket.

Frank was vainly trying to scramble to his feet, but every attempt met with a kick or blow that sent him toppling again. Then, as suddenly as they had appeared, the gas-masked thugs darted away through the smoke.

Joe picked himself up, clawed out a handkerchief to hold over his eyes and nose, and groped his way toward his brother. Frank met him, and hand in hand they ran from the smoke area. In the distance they heard a car start and drive off.

Frank and Joe finally reached clear air. Coughing, the boys slumped against a tree and looked at each other through swollen, red-rimmed eyes.

âWow! We fell into a trap that time, Frank!â

âSure did. Joe, we ought to get back to the car and radio the police.â

âOkay, but letâs wait till the smoke clears.â

Presently they were able to return to the convertible. Frank warmed up the short-wave radio and gave the police a description of the sedan.

Joe, meanwhile, was mounting the spare. âSorry I got us into this, Frank,â he apologized. âI shouldnât have said anything to Hirff about Tigersâ Bight.â

âNever mind. They still wouldnât have nailed us if weâd used our heads.â

âHow do you figure?â

âThat guy rifling our glove compartment was probably a decoy,â Frank reasoned. âIf he didnât find what he was after, Iâll bet his orders were to let us spot him. They knew weâd go after him, so they had the tire-puncture trick and the gas attack all set up beforehand.â

Joe shook his head ruefully. âBoy! Now I really feel like a chump!â

âDid they get your camera?â

âYes. Iâm glad it was insured!â Joe grinned. âBut thereâs one thing they didnât get.â

âWhatâs that?â

âTake a look in the glove compartment.â

Frank did so, then turned in astonishment. âThe film ! How did that get in here?â

âSimple. I unloaded the camera while you were wheeling after âem.â Joe chuckled as he wrestled the spare into the trunk. âI had a hunch there might be trouble if we caught up with those charactersââand the glove compartment looked safe because it had already been searched.â

âNice going, Joe!â

As they were driving home, Joe remarked, âHirff called the signals on that attack.â

âSure, but try and prove it. He probably phoned his pals the second we left the airport and has a nice, clear-cut alibi for himself.â

As soon as they arrived home, the boys developed the film and made an enlarged print of the chart. As expected, it showed the Bayport coastal area. A notch in the coastline south of Barmet Bay had been circled in pencil.

âItâs the place on Clams Daggettâs mapâTigersâ Bight!â Frank exclaimed, then frowned. âI donât get it, Joe. Hirff knew weâd heard about Tigersâ Bight, and we were bound to locate it. So why was he so eager to get the film back?â

âYouâre overlooking something, Frankâright here.â Joe pointed to an X mark near the bight, barely visible on the print.

Frank gave a whistle. âWonder whatâs there!â

âMaybe enough evidence to put the gang behind bars,â Joe surmised. âThis photo would link them to whatever that X stands for.â

âWow!â Frank was jubilant. âI have a feeling weâre really getting somewhere now, Joe!â

âIf only we knew what those words on Jackâs phone pad meantââAmethyst calling Seacat.â â

âSounds like a radio call,â Frank mused. âIt would tie in with our guess about âSeacat.â â

âIn other words, a radio call to a boat.â

âRight. But the âAmethystâ part stumps meâunless thatâs the name of another boatâor maybe of a plane thatâs doing the calling.â

âThatâs it, Frank!â Joe snapped his fingers excitedly. âIt could be a code name for Jackâs own planeâor even for Jack himself!â

âRight. Letâs assume Tom Lesterâs hunch is correctâthat Jack managed to worm his way into Hir$âs gang. And letâs assume your hunch is correct that he was flying to Tigersâ Bight.â

âOkay. So what then?â Joe asked.

âDonât you see? Maybe Jack was flying there on Hirffâs instructions. Hirff told him to contact a boat named the Seacat by radio and then rendezvous with it in Tigersâ Bight!â

âPerfect!â Joe exclaimed. âFrank, if Jack was flying a mission for the gang, that radio message wasnât sabotaged. It must have been interrupted accidentally.â

âIâll check right now!â Frank said. He called the Bayport radio station and learned that it, too, had experienced freakish transmission difficulties the day beforeâapparently due to sunspots.

âFrank, letâs go to Tigersâ Bight and find out what that X stands for,â Joe proposed. âWhile weâre at it, we may spot Jackâs plane!â

âOkay,â Frank agreed. âBut letâs call Dad first. He may be back at the hotel by now.â

The boys were able to contact Fenton Hardy. âHowâd you make out in Gary, Dad?â Frank asked.

âWe ran into a blank wall,â the detective replied. âThe getaway car was traced there. But Iâm sure now it was just a false scent to make us think the thieves had fled to that area to hide out.â

When Mr. Hardy heard about the Haley Building mystery and the vanished diamonds, he concluded that the same jewel thieves had struck again.

âSam and I had better fly back there as soon as possible,â he told Frank. âWeâll try to be in Bayport sometime tonight.â

Mr. Hardy listened with keen interest to Frankâs report about Al Hirff, the notation on Jackâs phone pad, the gas-bomb attack on the boys, and their theory about Tigersâ Bight.

After concluding the conversation, the boys drove to Bayport harbor. They rented a motorboat and started into the bay. As they passed the jetty, they sighted the Napoli, with Tony and Chet aboard.

The boys hailed one another, and brought their boats alongside. Frank told them where he and his brother were heading.

âWhy pay rent on that job?â Tony exclaimed eagerly. âIâll take you there in the Napoli!â

Frank considered a moment, then shook his head. âThereâs another job you can do.â

âName it.â

âWe have a hunch that âSeacatâ may be the name of the gangâs cabin cruiser,â Frank explained. âHow about cruising all the coves around here and see if you can spot a boat by that name?â

Tony and Chet agreed, and the Hardys resumed their course. Reaching the mouth of Barmet Bay, they headed southward along the coast. After a half hourâs run they sighted Tigersâ Bight.

âIf Tigersâ Bight is just a local nickname, I wonder how the gang picked it up,â Joe mused.

âThey must have heard it from some local boatman or fisherman,â Frank reasoned.

Joe slowed the motor as they cruised into the bight. The cove was wooded on all sides, with a strip of flat sandy beach extending for about a quarter of a mile. The rest of the shore was rocky.

âFrank, that beach would have made a good landing strip for Skyhappy Sal,â Joe suggested. âWhat say we take a look for plane tracks?â

âGood idea.â

Joe brought the motorboat in close and anchored. The boys pulled off their loafers and socks and waded ashore. The sand appeared unmarked.

âYou could still be right,â Frank told his brother. âThe tracks may have been washed out during high tide.â

Returning to their boat, the Hardys consulted their photographic blowup of Hirffâs chart. The X mark lay inland from the bight on a narrow creek which flowed not far from the beach. Aside from a few gulls screeching overhead and the noise of the surf outside the bight, the area was calm and silent.

Frank frowned at the racket of the motor as Joe steered toward the creek. âIf any of the gangâs around here, we sure wonât take âem by surprise,â he remarked.

Joe nosed the boat gently into the creek. Frank moored it to a rock and they headed inland on foot. The brothers had hiked only a short distance along the winding stream when they sighted a dilapidated cabin nestled among trees.

âSo thatâs what the X mark stood for!â Joe exclaimed.

The boys advanced cautiously to reconnoiter the cabin. Suddenly they were startled by the sound of a plane engine revving up along the bight. A moment later the plane soared into view among the trees.

âItâs Skyhappy Sal!â Frank yelled.

The craft was heading seaward. To the boysâ astonishment it banked and circled sharply, then came swooping in lowâstraight toward them! The pilot cut the motor, and the Hardys caught a fleeting glimpse of Jack Wayne and another man in the planeâs cabin. Jack waved to them frantically.

âDonât go into that cabin!â he shouted.

The pilot gunned the engine, trying to work up flying speed againâbut the plane dipped and went into a stall.

âHeâs going to crack up!â Joe yelled.

An instant later the boys heard a terrific impact and the crash of crumpling metal!

CHAPTER XV

Puzzling Reports

FEARING the worst, Frank and Joe ran along the creek bank. As they emerged from the trees, they saw that the plane had hit the beach about two hundred yards away. Its nose was high in the air and one wing had crumpled.

The Hardys ran toward the crashed aircraft. Jack was evidently still in the plane, but his companion had been hurled from the cabin by the force of the impact. He was getting dazedly to his feet and brushing off the sand that smeared him from head to foot. At the sight of the boys, the man began groping frantically on the ground.

âHe may be hunting for his gun!â Frank warned. âWeâd better nail him fast!â

Frankâs guess seemed to be correct, for as the Hardys closed in, he gave up his search and fled into the woods. Joe would have chased him, but Frank grabbed his brotherâs arm and pointed to Skyhappy Sal. Flames were licking the fuselage!

âNever mind that guy! Help me get Jack out!â

The right side of the plane, from which the gunman had been thrown, was uppermost. The door was hanging wide open. Frank climbed inside, careless of the sizzling flames. Jack lay wedged behind the control column, bleeding and motionless.

âHe risked his life to signal us!â Frank thought. âI sure hope heâs still alive!â

There was no time to be gentle. Frank maneuvered the limp form out as best he could. Legs first, Jack was passed through the cabin doorway Both the Hardys were streaming with perspiration as they lurched away from the plane, lugging the pilot between them.

At a safe distance from the wrecked aircraft, they laid Jack down on the sand and turned back to stare at Skyhappy Sal. The blaze was now crackling furiously.

âSome of the electrical gear must have shorted,â Joe said.

âWeâll never know,â Frank muttered. âOnce the fuel tank blows, sheâllââ

His words were cut short as the plane exploded into a ball of fire. A column of smoke and flame shot high in the air.

âWow! We made it just in time!â Joe gasped in a shaky voice.

The boys turned their attention to Jack Wayne. His face and shirt were streaked with blood from a scalp wound. Frank felt the pilotâs pulse and knelt to listen for a heartbeat.

âThank goodness! Heâs still alive!â Frank reported tensely.

Joe ripped off a piece of his own shirttail to make a bandage. Fortunately, although the pilotâs hair was matted with blood from the wound, active bleeding appeared to have ceased.

Frank wiped off Jackâs face with a scrap of cloth moistened with water. Presently the pilot stirred and opened his eyes. As he saw Frank and Joe bending over him, his lips twitched into a smile of relief.

âSure glad you boys are safe,â he murmured.

âGlad weâre safe!â Joe echoed. He flashed his brother a puzzled glance.

âMust have something to do with the cabin,â Frank said. âYou were trying to warn usâis that it, Jack?â

Their friend gave a faint nod. âI was waiting there with that other guy ... to meet the boss. Then he ... he got word by radio that you two might show up. Radio message said to booby-trap the cabin w-with explosive ... and pull out.â

âWait, letâs get this straight,â Frank put in hastily. âYou flew here because Hirff offered you a chance to join the gang?â

Again the pilot nodded.

âAnd your plane was hidden in the brash so no one would spot it?â Joe added.

âTh-thatâs right,â Jack mumbled. âWe were just about to leave when your boat pulled in. Barney, heâs the guy who was with me ... he said we should lie low till you were out of sight ... then take off ...â

Jackâs voice was getting weaker. Frank urged him not to talk, but the pilot, now lapsing back into unconsciousness, seemed not to hear.

âB-Barney was holding a gun on me ... test ing me to s-see what Iâd do. Only way I could warn you was toââ

Suddenly Jackâs head lolled to one side.

âHeâs passed out again, poor guy,â Frank said, checking the pilotâs pulse.

âHe saved our lives, Frank,â Joe murmured. âWith that cabin deserted, weâd have walked inside and been blown sky-high if Jack hadnâtââ

The wilderness quiet was suddenly shattered by the staccato noise of a boat engine. The Hardys leaped to their feet and saw their own motorboat shoot out from the creek! Aboard was the man who had been hurled clear of the planeâthe man whom Jack had called Barney.

âWhat a couple of nitwits we are!â Joe burst out furiously. âWhile we were talking here, we let him circle through the woods and grab our boat!â

There was no possible chance of retrieving the craft. It was already picking up speedâheading out of the bight toward the open sea.

âThe prize boner of all time!â Frank groaned. âWeâre stranded here, Joe! And Jack needs medi cal attention!â

The photographic print of the map was in the boat, and neither boy could remember any inland details, but Joe felt sure the nearest road was at least ten miles away.

âLooks as though we have two choices, Joe,â Frank said thoughtfully. âWe can wait here till the folks back in Bayport get worried and come looking for us. Or one of us can try to find a road and flag down a car for help.â

Joe shook his head. âPretty long shot. Whoever went might not be able to find his way through the woods before dark. But thereâs one other possibility, Frank.â

âSuch as?â

âTry to get into the cabin without exploding the booby trap and use the gangâs radio.â

âYouâre right! I never thought of that.â Frank rubbed his jaw worriedly and considered.

The boysâ debate was cut short as they saw a small cruiser heading into the bight. Frank and Joe jumped up and down, yelling and wigwagging their arms, but they soon realized the signals were unnecessary. The cruiser evidently had been attracted to the scene by the smoke and flame of the burning airplane.

The skipper of the cruiser brought his craft in close to the boys and shouted through cupped hands, âWhat happened? Do you need help?â

âWe sure do!â Frank yelled back. âA plane crashed and the pilotâs injured! Weâre stranded here! Can you get us to Bayport?â

âYou bet I will!â the skipper replied heartily.

Normally the Hardys would not have risked moving a man in Jackâs condition. But they felt they had no choice. Using a tarpaulin from the cruiser as a makeshift stretcher, they carried him through the shallow water and loaded him gently aboard the boat.

Mr. Webb, the elderly, white-haired owner of the cruiser, revved his engine and they started out of the bight.

âToo bad I have no radio, boys, or we could call ahead and have an ambulance waiting.â

âWeâre mighty grateful, anyhow, sir,â Frank replied. âIf you hadnât come along, I donât know what we would have done.â

There seemed little chance of sighting or overtaking the stolen motorboat. But as they approached the bay, Joe thought he glimpsed the craft and asked to borrow Mr. Webbâs binoculars.

âThatâs our boy, all right!â he said a moment later, passing the glasses to Frank. âHeâs heading somewhere near Sea Gull Cove!â

Minutes after they docked, an ambulance came screeching to the scene in response to a phone call by Frank. An intern gave Jack emergency treatment. Then the injured pilot was transferred from the boat on a stretcher. The Hardys followed in their convertible as the ambulance sped off, siren wailing.

From the hospital, Frank telephoned Police Chief Collig and made a full report. The chief promised to have state troopers dispatched at once to the cabin to disarm the booby trap and search for clues. He also promised an immediate search for the stolen boat.

âIncidentally, Frank,â Collig went on, âTiffman, the messenger, and the watchman were all given lie-detector tests this afternoon.â

âHowâd they make out?â Frank asked.

âBelieve it or not, all three are in the clear.â Collig sounded thoroughly irritated and baffled. âI donât know what kind of trick was played, but Iâll get to the bottom of this yet!â

After hanging up, Frank called the boat livery and explained what had happened. âIâm sure the police will recover it,â he added.

A few minutes later a doctor stepped out of the emergency ward. âYour friend seems to be in fair shapeâno broken bones,â he told the boys. âHowever, heâs still unconscious and may have a concussion.â The Hardys felt relieved that the news was no worse.

It was now past six oâclock, and the boys were due home for dinner. But Frank had an idea which he urgently wanted to check out with Mike, the night watchman at the Haley Building. He telephoned home, then the brothers drove from the hospital.

âWhat can I do for you, boys?â Mike greeted them. âStill huntinâ clues to what happened here last night?â

âWell, sort of,â Frank said. âIâd like to ask you some questions and find out exactly what took place before and after the messenger came.â

âOkay, shoot!â

Probing insistently, Frank had the watchman go over everything that had happened the night before. It turned out that Mikeâs recollection was hazy for two periods of about twenty minutes eachâone around seven oâclock and the other around eight-forty-five.

âGuess I mustâve dozed off,â the watchman admitted a bit shamefacedly. âI remember cominâ to with a start both times.â

As the boys left the building and got into their car, Joe remarked, âSo he blacked out twice! That sounds like the same method used on all the other jewel robberies!â

âWhich backs up Dadâs hunch.â Frankâs voice was tense. âJoe, I think I can explain the mystery of what happened here last night!â

CHAPTER XVI

Riddle With Three Answers

JOE glanced eagerly at his brother as their convertible pulled away from the curb. âLetâs hear your theory, Frank!â

âChief Collig says the lie-detector tests show that all three people involved are telling the truth,â Frank began. âThe watchman, the messenger, and Mr. Tiffman.â

âSo?â

âTherefore,â Frank continued, âwe can assume the watchman did take the messenger up in the elevatorâbut not to the fifth floor. And OâBannion did deliver the gemsâbut not to Tiffmanâs office.â

âNow wait a minute,â Joe said. âIf OâBannion didnât take the diamonds to Tiffmanâs office, where did he take them?â

âTo an office on the sixth floorâor possibly the fourth.â

âHow do you figure that?â

âThe watchman blacked out twice,â Frank replied. âDuring that time, someone could have tampered with the elevator controls and also with the office numbers.â

Joe frowned. âSo Mike thought he was letting the messenger off on five. But actually it was one floor higher or lower.â

âRight â

âCould the elevator setup actually be doctored to fool the operator that way?â Joe asked.

Frank nodded as he braked for a red light. âIâm sure it could, Joe. That elevator is a push-button job with solid doorsânot an old-fashioned cage with manual control. A smart mechanic could make the elevator stop at the wrong floor just by switching a few wires beforehandâand the person inside wouldnât know the difference-even the watchman himselfâunless he timed the ride.â

âHow about when the messenger rang to go down?â Joe asked.

âThat makes a light flash on the control panel,â Frank replied. âBut letâs say the wiring had been tampered with. OâBannion rings from Six, but the light shows Five. Mike pushes the button for Fiveâbut the elevator actually goes up to Six, where OâBannion is waiting. Neither one realizes anything is wrong.â

âWow! Pretty slick!â Joe exclaimed. âAnd the office numbers were switched too, eh?â

âYesâprobably by a confederate, to speed up the job. The doors arenât glassed, with the numbers and names painted on them. They have metal numerals and name plates screwed on.â

âWhich would be easy to change,â Joe agreed. âThe crooks could have had duplicate name plates made up beforehand to match the ones on Five.â

âAnd they wouldnât have needed to substitute all of them,â Frank added as he swung off Main Street into the residential area of Bayport. âJust on the doors the messenger would see. And, of course, substitute fives for the sixes.â

âSounds foolproof,â Joe said. âOne of the crooks waits in the phony office and takes the gems. Then after the messenger leaves, they black out the watchman again and switch everything back the way it was before.â

âRight,â Frank replied. âNow the question isâhow do the crooks do their blackout trick?â

âIâve been thinking about that,â Joe brooded. âFrank, that may be where Professor Darrow and his scientific know-how come into the picture.â

âYou mean heâs in cahoots with Strang?â

âMaybe.â Joe shrugged. âPerhaps heâs even trying to work off a grudge against society because no one would back his research, or he may have been brainwashed.â

âCould be,â Frank agreed. âHe sounded a bit odd from what Dean Gibbs told us.â

Frank swung into the Hardysâ drive. âAnother thing, Joeâwhat did that remark you heard on the tunnel phone mean?â

âAbout the âdisappearing floorâ? I have a hunch it referred to the Haley Building job.â

âThatâs one possibility. Actually, there are three âdisappearing floors.â Oneâthat phonily numbered floor at the Haley Building. Twoâthe hinged tiled summerhouse floor. And threeâthat invisible floor of Old Man Perthâs bedroom-study at the mansion.â

Joe chuckled. âA riddle with three answers!â

Aunt Gertrude suddenly thrust her head out the side door. âAre you expecting dinner to be served in the car? Foodâs cold already!â

âSorry, Aunty,â Frank said. âItâs my fault.â

Miss Hardy was curious about the latest developments in the case. At the table she listened eagerly as the boys told about the startling events at Tigersâ Bight. Both she and Mrs. Hardy expressed concern over Jack Wayne.

âOh, I hope there wonât be any aftereffects,â said the boysâ mother.

Before the brothers could be served dessert, Tony and Chet arrived with more exciting news.

âWe found a cruiser called the Seacat!â Tony announced breathlessly. âIt looks like the one we saw before that frogman attacked Joe!â

âWhere is it now?â Frank asked.

âIn one of those coves just off Shore Road,â Chet blurted out.

Aunt Gertrude sputtered indignantly as Frank and Joe hurried away without waiting for any pie Ã  la mode. They jumped into their convertible and followed Chetâs jalopy.

Dusk was falling as the four friends pulled up near the cove. An old, rather battered-looking coupÃ© was parked among the trees.

âMust belong to someone on the cruiser,â Tony speculated. âThereâs nothing else around here.â

âI have an idea,â Joe said. âLet me take the convertible, Frank. Chet, you park in that next grove, and Iâll meet you fellows in a few minutes down in that clump of willows on the cove.â

The others agreed, wondering what he had in mind. After Joe had made a U-turn and driven off, Chet parked his own car, then started down the hillside toward the cove with Frank and Tony.

The three boys hid among the willows and looked out across the water. The cruiser lay silently at anchor amid the deepening twilight, with a dinghy tied alongside. A faint, wavering light came through the cabin portholes.

Ten minutes went by. At last Joe joined them.

âI borrowed Dadâs radio signal-sender,â he explained, âand attached it to the axle of that coupÃ© so we can trail it.â

âSmart idea,â Frank said approvingly.

A few more minutes passed. Then the light aboard the cruiser went out. Presently a shadowy figure emerged from the cabin, but it was now too dark for the boys to make out the manâs features. He glanced around furtively, then climbed into the dinghy and began rowing ashore.

âHe sure acted sneaky,â Tony whispered.

âHeâs probably not the owner,â Frank surmised. âIâll bet he had no right to be aboard.â

The man rowed across the cove, moored the dinghy to a tree, and started up the hillside.

âHe must be the person who parked that coupe,â Joe muttered excitedly.

The boys hurried back to their own cars. Joe had parked in the grove, close to Chetâs jalopy. Almost instantly they heard the coupÃ© start up, and a moment later it drove past. Joe switched on the special receiver for the radio-tailing device. A low, steady whirring wail issued from the speaker.

âOkay, letâs go!â he told Frank.

The convertible swung out onto the road. Chetâs jalopy followed. Frank kept his headlights dimmed and stayed a safe distance behind the coupe. It circled Bayport and turned onto the road the black sports car had taken three nights earlier. Joe traced the coupÃ©âs course by manipulating a loop antenna.

âHeâs going to the Perth mansion!â Joe exclaimed as a sudden fade in the radio howl announced a turn by their quarry.

The boys pulled off the road and waited a few minutes so as not to betray themselves. Then they, too, entered the dirt lane. After parking in some shrubbery, they began searching for the coupe. Frank soon spotted it standing half-hidden among some trees farther down the lane.

âLooks as though heâs trying to stay undercover himself,â Tony muttered.

âIâm sure heâs not one of Strangâs men,â Frank agreed as Joe jotted down the license.

âHow are we going to find him?â Chet asked.

âScout around and use our eyes,â Joe replied.

The four boys started up the slope. They all swung around with a start as a bloodthirsty snarl sent their pulse rates skyrocketing. Frank had to clamp a hand over Chetâs mouth to prevent the stout youth from shrieking.

âSteady, pal! Thatâs just a mechanical spook houndâto scare off people like us.â

Chet gulped as the fiery-eyed hound snarled again.

âIt just succeeded with one person!â the fat boy announced and started back down the slope. Frank calmed him and they went on. Tony and Chet waited in the shadows as Frank and Joe made their way to the house. They had just reached the porch when they heard a muffled âSsst!â from Tony and turned.

A white phantom was moving toward the house.

âThe galloping ghost!â Joe gasped.

The boys went racing toward it, but the ghostly figure detected their approach and Bed.

âThat ghost must have eyes in the back of his head!â Joe muttered angrily, still running.

The specter soon disappeared from view among the trees. Frank acted on a hunch. He shortcut back to the coupÃ© and hid among some bushes. A white figure suddenly loomed out of the darkness. It headed straight for the car and yanked open the door. Before the phantom could climb inside, Frank pounced on him!

The spook-masquerader battled wildly, but the other three boys quickly arrived on the scene and helped Frank pin him against the car.

âPretty solid for a ghost!â Chet remarked.

âNot as solid as you,â Joe quipped. âBut thereâs flesh under that spook costume!â

âLetâs have a look at him,â Frank added, and pulled off the prowlerâs hood.

CHAPTER XVII

The Second Specter

CHET let out a gasp of surprise as Tony shone a flashlight at the manâs face. âItâs that creep we picked up unconscious the other night!â

âAnd also the thief who stole Iola and Callieâs amethyst,â Frank added.

The man cowered in the glare of Tonyâs beam. âPlease, boys,â he whined, âI meant no harm. This ghost masquerade was just intended as a hoax. Nothing more than a joke.â

âSome joke,â Tony said dryly.

âHow about stealing that amethyst?â Chet growled. âThat was a joke too?â

The manâs face turned pale. âNo, itâit was wrong of me, tricking you with that oil smudge and snatching the stone right out of your house.â He wet his lips nervously. âBut I had to have it! By rights, the stone belongs to me.â

The boys were puzzled.

âHow does it âbelongâ to you?â Joe asked.

The man squirmed uncomfortably. âIt doesnât matter,â he mumbled, âYouâll find what youâre after in my right-hand coat pocket.â

Joe reached inside the white robe. A moment later his hand emerged holding a purple stone.

âThe amethyst!â Chet exclaimed. Joe turned it over to him to give back to the girls.

âYou still havenât answered my brotherâs question,â Frank said in a cold voice. âWhy did you say the amethyst belonged to you?â

The prisoner had an angry look, like that of a trapped animal. âI told you it doesnât matter!â he retorted. âI know what you boys are up to! Youâre trying to worm information out of me, hoping you can get all the stones for yourselves!â

âNow listen,â Frank snapped, âI donât know what you mean by that remark, but youâd better talk fast or weâll call the police! I think we should, anyhow.â

âNo, no! Please!â The prisoner seemed to crumble. âI canât afford to go to jail nowâthereâs so much to do! I can explain. Iâll tell you whatever you want to know.â

âYou can begin by answering Joeâs questionâand then tell us why youâve been prowling around in that spook getup.â

âAll right.â The man gulped and tried to pull himself together. âMy name is Karl Nyland Jr. Years ago, my father discovered an amethyst lode somewhere near Bayport. He went to old Jerome Perth for financial backingâthey even signed a partnership agreement. But that swindler, Perth, double-crossed him!â

âHow so?â Frank asked.

âPerth bought the site in his own name, then kept stalling my father offâsaid he was waiting for a geologistâs report. Finally my father got fed up. They quarreled and Perth had my father thrown out of the mansion. But first Perth taunted him. He said the partnership papers, and some amethysts my father had brought him, were kept in a place outside the mansion where anyone could get at themâbut my father wouldnât be smart enough to find it.â

âBoy! Sounds as if Perth was a real snake in the grass!â Tony muttered.

âThat man was evil,â Nyland declared, âbut he got his just desserts. The quarrel brought on a heart attack and he died the next day.â

âDidnât the partnership papers turn up when the old manâs estate was settled?â Frank asked.

âNo, his lawyers claimed that no such papers, nor the amethysts, were among Perthâs effects. My father kept searching secretly for a long time after that, but he never could find the hiding place.â

Joe snapped his fingers. âHe must have been the ghostly figure that people thought was haunting this place!â

âYes, he was searching here the night the nephew died,â Nyland admitted. âThatâs what gave him the idea of dressing as a ghost. He thought it might help to scare tenants away and keep the mansion unoccupied until he could locate the secret cache. But he never found it.â

âAt least his scheme to scare people away worked,â Chet put in. âAnd now youâve been trying the same stunt?â

Nyland nodded guiltily. âI received a bad electrical shock when I was searching here the other night. Thatâs when you boys found me unconscious. Since youâd seen my face, I decided Iâd better use a ghost costume as a disguise, in case you came back to look for me.â

âHow come you waited so long to begin searching?â Joe inquired.

âI was a child living with relatives in another state when Perth swindled my father,â Nyland explained. âIt was only recently that I ran across my fatherâs diary and read the whole story. My wifeâs been very ill, and I was in debt from the hospital billsâso I decided to come to Bayport and try to find the lode and the partnership papers.â

âSounds like a wild-goose chase,â Frank said.

The man nodded. âThatâs just what itâs been. All I have to show are these.â The man reached into his pocket and pulled out a dozen small metal disks. Each bore a picture of a violet above a dragonâs head I

âPerthâs lucky pieces!â Joe exclaimed. âWe found one near the mansionâyou must have dropped it there!â

âCould be,â Nyland admitted.

âDo you know what the design was supposed to signify?â Frank asked.

âNot really,â Nyland said, then added ruefully, âTo me, the dragon is Perthâand the violetâs a symbol of the lovely purple stones he tricked my father out of.â

Joe frowned. âWas there only one copy of the partnership agreement?â

âExactly. Perth was sly about that. My father foolishly trusted him and didnât insist on two copies being drawn up.â

âThen why wouldnât Perth simply destroy the agreement when the deed was in his name?â

âHe was using it to soft-soap my father and keep him quietâalso to keep him on a string. You see, my father had made two earlier gem strikes for a mining company. Perth no doubt hoped he might make other valuable finds. And Iâm sure Perth was cruel enough to keep the agreement after their quarrelâjust to tantalize and torment my father.â

âYou have no idea where the amethyst lode was located?â Joe asked.

Nyland shook his head dejectedly. âNo, Perth owned a great deal of property, but it was all sold off after his death. And the diary didnât say. Thatâs why I shadowed those two girls after I overhead them telling the gem-shop proprietor about finding a large amethyst. I hoped they might lead me to the lode.â

âWhat were you doing aboard that cruiser tonight?â Tony inquired.

Nyland shrugged. âJust a hunch. Thereâs something strange about those people living at the mansion now. This afternoon I saw two of them in town and heard them mention the word âamethyst.â I thought maybe they had found the papers relating to the lode, so I shadowed one of them. He went to that boat, and after he left, I climbed aboard myself. But it was a waste of timeâI found nothing.â

Nylandâs shoulders sagged. Half sobbing, he began to tell the boys about his wifeâs illness and the debts that had made him desperate. He pleaded with them not to turn him over to the police. The Hardys, Chet, and Tony felt perplexed and embarrassed. They decided to leave the decision to Mr. Hardy.

Suddenly a light went on in an upstairs window of the mansion. Joe exclaimed, âItâs the window where we spotted that man who looked like Professor Darrow! Frank, letâs stay hereâwe may see him again!â

Frank glanced at Chet and Tony. âDadâs due in tonight. Would you two take Nyland to our house and keep him there till Dad arrives?â

âSure. I can call my folks,â Tony replied.

âSame here. And maybe your Aunt Gertrude will make us all a snack,â Chet said hopefully.

Nyland, anxious to avoid arrest, agreed to accompany them with his hands tied and to make no trouble. All three went off in Chetâs car.

âThe manâs odd, but I think he was telling the truth,â Frank said. âHe sure sounds as if heâs been under a nervous strain.â

The Hardys started back up the slope. Cautiously they began making their way through the wooded grounds toward the mansion.

Suddenly there was a weird scream from close byâthen another, weaker scream, ending in the same gasped-out words they had heard before:

âTh-th-the floor!â

Frank and Joe froze. âItâs only a trick,â Frank muttered as they started forward again.

They were nearing the house when both boys went cold with shock. A glowing white figure had risen from the ground!

âWe caught the spook already,â Joe whispered.

âItâs a fake, Joe.... It must be a fake!â Frank stared in horrified fascination.

The thing was moving toward them, flapping!

Resisting an impulse to run, the Hardys closed in. They clutched at the specter. Joe gave a chuckle of relief as he felt the wire framework underneath. It was covered with some kind of synthetic cloth, which evidently had been dipped in white phosphorescent dye.

âJust a pop-up scarecrow, Frank! We must have stepped on the release mechanism back there.â

âRight, Joe. And look at the wheels. The breeze blew it toward us!â

They went on. In the shadow of a tree they paused and looked up at the lighted window. Shelves with bottles and test tubes, and some electrical apparatus, could be seen.

âA laboratory!â Joe murmured.

Behind the shaded windows on the ground floor a radio was blaring dance music.

Suddenly a man moved into view at the upper-floor window. Bald and bespectacled, he was holding an open book in one hand.

âThere he is!â Frank whispered.

âThatâs Darrow, all right,â Joe agreed. âIf only we could talk to him!â

âFat chance with Strang and his gang around. Anyhow, weâve seen all we need to. Letâs go home and wait for Dad.â

Turning, the brothers started back across the grounds to their car. Halfway down the slope, they heard the screams and the choking voice again.

âHold it, Joe,â Frank hissed. âThat tiled floorâs around here somewhere. Did you notice that we always hear the screams near here?â

The boys shone their flashlights carefully about the ground. Suddenly Joeâs beam disclosed a small metal object sticking up from the grass.

âIâll bet thatâs it, Frank! Must be some kind of sensorâmaybe infraredâthat triggers off a tape recording when anyone comes near.â

Joe moved closer to examine it. Again the voice shrieked! Startled, Joe backed off hastily and his foot struck a rock.

Frank gave a cry of dismay as the ground gave way under his feet. Down he plunged!

âThe tunnel exit!â Joe exclaimed. âMy foot hit a rockâsame thing that happened last night. That must be what opens it from the outside.â

âRight. And look at all this sod and brush that fell in with meâthey do camouflage the tiled floor.â Frank shone his flashlight into the tunnel. âWonder if we could get into the house this way, past Strang and his henchmen, and talk to Professor Darrow?â

Joe leaped down beside Frank. âIâm game! Letâs find out where the tunnel leads!â

CHAPTER XVIII

A Strange Machine

FRANK had been only half serious when he spoke of trying to enter the house through the tunneL But Joeâs excitement communicated itself to him. This might be a chance to get information or a clue that would break the case!

âOkay. Letâs take a look.â

They started into the tunnel, one behind the other. Frank led the way, probing the darkness with the yellow beam of his flashlight.

âWatch that intercom!â Joe warned. âWe donât want another chat with Waxieâs pal!â

The brick-walled passageway went on for hundreds of feet. The boys came at last to a door. It had a lock but opened freely when Frank tried the knob. âIt must unlock automatically when the tiled floor opens,â he whispered.

âIn that case, why the intercom?â

Frank shrugged. âSomeone might want to hide in the tunnel but still be able to communicate with the house. Or maybe they post a lookout at the tunnel exit sometimes and have him report back by phone.â

The boys played their flashlights around. âWe must be in the basement of the mansion,â Joe murmured.

The huge, cement-floored area was dank and musty. There was a coalbin, a grimy-looking, cobwebbed furnace, and an air-conditioning unit that looked brand new. Far at the rear was a flight of stairs leading upward.

Frank asked his brother, âShould we risk it? Or turn back?â

âDonât be silly! Weâre going to talk to Professor Darrow, remember?â

The boys walked cautiously toward the stairway and tiptoed up. They found that the first flight ended at the kitchen of the sprawling mansion. From here another flight led upward. The stairs creaked under the boysâ tread, but fortunately the radio music racketing in the ground-floor front rooms covered their noise.

Reaching the upper floor, the boys went along a corridor toward the front of the house. The hallway twisted and turned as if the mansion had been designed with an eccentric floor plan. After passing several doors, the Hardys stopped at one which showed light underneath.

âThis must be the laboratory,â Frank whispered.

Joe held up crossed fingers. âOkay. Letâs find out.â

Frank opened the door. Professor Darrow was holding a test tube of colored liquid up to the light. He turned as the boys enteredâand gave such a violent start that the liquid splashed on his workbench!

âProfessor Darrowâ?â Frank inquired. Joe closed the door softly behind them.

The scientistâs hand trembled as he placed the test tube in a rack. He stared at the Hardys through his steel-rimmed eyeglasses and his eyes were full of fear.

âWho are you? What do you want?â he blurted out in a shrill, staccato voice.

The muffled strains of the radio music could be heard through the floor.

âWeâre Frank and Joe Hardy, sir,â Frank began. âOur father is Fenton Hardy.â

He assumed the name would be familiar to a crime-detection expert. But Darrow glared at them, giving no sign of recognition.

âFenton Hardyâthe private investigator,â Joe emphasized. âMaybe youâve heard of him.â

âMaybe.â The scientistâs eyes bored through the boys. He wore a white lab coat and his wispy fringe of gray hair frothed out wildly around his narrow skull. âWhy did you come here?â

âDean Gibbs of Western State asked us to locate you andââ Frank started to explain.

âHe would! Youâve come here to spy on me!â

âThatâs not true!â Frank exclaimed.

âThe dean wired us on behalf of your sister,â Joe put in hastily. âSheâd like you to get in touch with her. Sheâs probably worried because she hasnât heard fromââ

Joe broke off suddenly as he noticed the professorâs hand inching toward a strange device on his workbench. It looked somewhat like a round, portable electric heater.

âLook out, Frank!â

Joe leaped clear in the nick of time as Professor Darrow snatched up the device. But Frank did not react fast enough. A dazzle of light flared from the machine. Instantly Frank stiffened and froze statuelike.

He had blacked out!

An electric cord ran from the machine to a wall socket. Joe yanked the plug before Darrow could aim the device at him.

âHelp! Help!â the professor shouted.

Joe glanced around frantically. The radio music from below had stopped. A moment later came the sound of feet pounding up the stairs!

âStrang and his boys!â Joe thought. âIâll have to duck fast! But where?â

Suddenly Darrow lunged at him and tried to pin the boyâs arms. Joe wrenched free and gave the professor a hard shove that sent him reeling backward. Darrow crashed into a corner of the workbench and went down in a cascade of glass tubing, retorts, and other laboratory apparatus.

Like a flash, Joe darted out through a doorway that led to an adjoining room. The door slammed behind him just as Strang and several henchmen came surging into the laboratory.

âThat way!â Darrow shrilled, pointing in the direction of Joeâs flight. âThrough that door!â

The gang rushed through a maze of connecting rooms. Joe, concealed behind the heavy, dark-red window drapes in the room next to the lab, could hear Strang barking out orders.

A moment later the master jewel thief strode past Joeâs hiding place on his way back to the laboratory. Through the open doorway, Joe heard him talking to the professor.

âYes, I know the boy. Recognized him at once,â came Strangâs voice, evidently referring to Frank. âHe and his brother are the sons of a clever spy who must have been sent to Bayport purposely to steal your invention.â

âJust what I feared!â Darrow replied. âThen itâs not true that theyâre connected in any way with Fenton Hardy?â

âCertainly not! In fact, Hardyâs now on my payroll, working undercover to safeguard your research.â Strangâs voice became firm and persuasive. âDonât worry, Professor! My men are bound to catch the other boy. Then weâll hand them both over to the FBI.â

âFrank, look out!â Joe yelled

âI certainly hope youâre right!â Darrow sighed heavily. âFirst the university authorities and jealous colleagues blocked my research grant at school! And now spies hounding me!â

âBy the way,â Joe heard Strang ask, âhow deeply did you black this kid out?â

âJust a light dose. But it should hold him long enough toââ

A loud alarm bell rang on the first floor, cutting short the professorâs words. Both Strang and Darrow dashed from the lab.

Joe waited until he heard their steps fading down the stairs. Then he burst from the drapes and rushed into the laboratory. Frank was still rigid. Joe filled a beaker with cold water from the workbench sink faucet and flung it in his brotherâs face. Frank seemed to shudder.

âFrank! ... Frank, can you hear me?â

Joe shook his brother and gave him several light slaps. Gradually Frank came out of the trance but appeared to have no recollection of what had happened. Joe explained hastily, adding, âStrang has the prof convinced that heâs surrounded by spiesâincluding us. An alarm just went off downstairs, and theyâve gone to investigate.â

Frank was still a bit dazed. âI must have been blacked out by the same device used in the jewel thefts, Joelâ

âSure, and Darrow thinks we came to steal it. We must find a way out of this place!â

âWait a second, Joe! That alarm you mentioned could have been Dad coming hereâmaybe even the police!â

âRight,â Joe agreed. From the sounds he had heard, he knew there must be a front stairway. The Hardys soon found it and strained to hear what was going on below.

âHere they come now!â. Strang was saying. âLooks as though theyâve nabbed whoever triggered the alarm!â

Frank and Joe leaned around the corner of the stair well and peered down into the front hall. Strang was at the front door with Professor Darrow. Presently three of Strangâs henchmen came in, prodding a burly prisoner at the point of a gun. Their captive had crew-cut hair and wore a gaudy plaid sport coat.

âDuke Makin!â Joe whispered in amazement.

âNo sign of that kid who got away, boss,â the gunman reported. âBut we caught Makin here snooping around outside.â

âGood work, Barney!â Strang said approvingly.

âBarneyâs the man who was with Jack Wayne at Tigersâ Bight!â Frank murmured in Joeâs ear.

Duke Makin looked self-assured, which appeared to infuriate Strang.

âI warned you once before, Makin, to keep out of my hair!â the jewel thief rasped.

Makin laughed contemptuously. âAnd I told you, Strang, that Iâm dealing myself in on this jewel racket of yours.â

âYouâre not muscling in on anything, Makin, except big trouble.â

Again Makin laughed. âYouâre the one whoâs got trouble. After you learned Fenton Hardy was on your case, a pal of mine in Chicago found out he was there. I asked my pal to tip off Hardy about the Haley Building job. How did I know about it? I overheard you blokes talking after you cased Tiffmanâs office. And thereâll be more tip-offs if I donât collect a share on every jewel haul you make from now on. I want to know what your blackout gimmick is, too.â

âWhatâs he talking about?â Professor Darrow asked Strang. âWhat does he mean by âevery jewel haul you makeâ?â

âGet back up to your lab, Professor!â Strang ordered roughly. âThis man is another foreign agentâheâs simply trying to pull the wool over your eyes. Iâll handle him!â

Darrow obeyed meekly, but he looked bewildered as he started up the steps. Frank and Joe shrank back into the shadows. Darrow reached the top of the stairs and turned toward his laboratory without noticing them.

Meanwhile, Makin had resumed his sneering argument with Strang. âI mean business!â

âShut up!â Strang exploded. âWe know you conked Waxie at the airport and swiped those amethysts from my carâbut itâs the last trick youâll pull, Makin! Take him to our âguest room,â boys. Iâll attend to him later, after we find the other kid!â

They herded Makin off toward the rear of the house. Frank and Joe tiptoed cautiously down the stairs, hoping to make a break through the front door.

But suddenly Darrow called from his laboratory, âThat boy we left in hereâheâs gone!â

With a snarl of rage, Strang came charging back into the front hall toward the stairway. Before the Hardys could retreat, he had spotted them!

CHAPTER XIX

Jewel Cache

FRANK and Joe ran wildly up the steps, two at a timeâthen fled down the corridor to their right, away from the laboratory. Below, Strang had just gained the stairway and was starting up in pursuit, bellowing to his men for help.

Selecting a room at random, Joe flung open the door and the boys darted through, slamming the door behind them. Here, too, the rooms seemed to interconnect in mazelike fashion.

âGood thing Perth built such a crazy house!â Frank panted, as they darted from one room to another.

The pounding footsteps of their pursuers could be heard from various directions as if the men were spreading out. But the mansion was immense, and the boys managed to reach the back stairway and dart down to the ground floor without being seen. Joe tugged at the back door which led to a rear porch, but it refused to budge.

âThey must have locked it when they were searching for us earlierâto keep us from getting out!â he muttered to Frank. The tunnel now seemed to be their best hope.

Halfway down the stairs to the basement, the boys saw A1 Hirff entering through the tunnel door. With a shout, he ran toward them. Frank and Joe fled back up the stairs. In the kitchen Frank grabbed up a garbage container and flung it toward the stair-well doorway. Then the brothers raced through a side hallway toward the front of the house.

Crash! They heard Hirff stumble over the garbage container.

A moment later an angry voice began shouting orders. It sounded like that of Strang. Steps came pounding down the front stairway, cutting off hope of escape through the front door.

âIn here!â Frank urged, pausing at a room on the left. He turned the doorknob and the brothers slipped inside, went through a small room, opened another door and entered a larger chamber.

In a few moments the door to the Hardysâ hiding place was jerked open again. Noel Strang flicked a switch and glanced hastily around. âThey must have made it out the front door!â he exclaimed to someone in the hallway. The light went out again, the room door was shut, and footsteps hurried off.

Frank and Joe emerged from behind the heavy window draperies. They dared not switch on their flashlights, but gradually their eyes became accustomed to the darkness.

âItâs Jerome Perthâs room,â Frank said. âThe same one we saw from outside!â

âBut now the floor feels solid,â Joe murmured.

Frank was frowning as he peered about the room. âJoe, do you notice anything funny about this furniture?â

âNo. What?â

âExcept for that chair at the desk, every single piece of furniture in the room is placed smack up against the wallâeven the armchairs.â

âThat is odd, Frank,â his brother murmured. âDoes that suggest something to you?â

âIt sure does. It suggests that the furniture may be bolted to the wall!â

Frank tried to move an armchair, the desk, and a wardrobe. None budged!

âWell, this explains one thing,â he remarked. âWe know now how the furniture was able to stay suspended in mid-air when the floor wasnât there.â

âWasnât there?â Joe echoed. He was examining the way in which the headboard of the bed fitted flush to the wall. He spoke over his shoulder. âYou mean you think the floor of this room really does disappear?â

As Joe turned to face Frank, his elbow rubbed against some ornamental carving in the wall paneling. The next moment both Hardys gasped.

The floor was sinking straight down under their feet!

âWhat did you do, Joe?â Frank exclaimed.

âSearch me! My elbow just brushed the wall somewhere up there by the light switch. There must be a hidden push button or something that operates this floor!â

By this time, the whole floor had descended like an elevator to basement level, carrying the boys and the unbolted desk chair with it. A familiar, musty odor came suddenly to the boysâ nostrils.

Frank turned on his flashlight and beamed it about the walls. To his right was a moldering wooden door. This was the window side of Perthâs room.

âAn entrance to the tunnel!â Joe whispered.

âDid you say thereâs a light switch up there by the bed?â Frank inquired.

âYes, probably a two-way switching arrangement, so the light can be turned on or off either from the doorway or from the bed.â

âJoe, I think I can explain how Perthâs nephew was killed!â Frank said excitedly.

âHow?â

âRemember, the nephew only lived in the mansion for a few days before his death. He probably never discovered the secret of this sinking floor.â

âWouldnât he have been curious when he saw that the furniture in his room was bolted to the walls?â

âMaybeâif he noticed. But his uncle had been a queer old cuss, anyhow. And evidently the servants didnât know the secret of the room, either.â

âNo, I guess they didnât, if they never told about it,â Joe agreed. âBut I wonder how come they never touched the switch accidentallyâsay while they were cleaning the wall paneling.â

Frank shrugged. âMaybe Old Man Perth told them not to clean itâor to use only a feather duster.â

âOkay, Iâll buy that. Go on.â

âWe know that Nylandâs father, Karl Nyland, was snooping about the grounds the night the nephew was killed. It could be that he made a noise outside the windows, and the nephew heard him and woke up.â

Joe nodded. âSounds reasonable. So?â

âSo the nephew gropes in the dark to turn on the light switchâand in doing so, accidentally presses the floor button, but doesnât know it.â

âWow! I get it!â Joe blurted out. âThe floor starts sinking, but since the furniture is still up there, he doesnât realize what has happened!â

âRight. So he jumps out of bed, falls clear down to the basement, and fractures his skull, poor guy! Then later, when the servants came to investigate, the opening of the anteroom door raised the floor back to its normal level.â

âIâll buy that.â Joe nodded. âBut what if Perth had to get the floor back up from the basement? How would he do that?â

âEasy, I think. He probably had a timer set that automatically raised the basement floor if the anteroom door was out of action.â

âSure,â Joe agreed. âThat would be a natural feature if Perth designed this setup as an emergency escape systemâliving in fear of his life as he did.â

âExactly,â Frank said. âIf any of his swindle victims ever forced their way into the mansion to get revenge, Perth could lower the floor to the basement and duck out through the tunnel. If the assassin actually broke into his room, heâd find it empty, the windows locked from the inside, and no trace of Old Man Perth!â

âFrank, Iâll bet youâve solved the mystery!â Joe said enthusiastically. âEverything fitsâeven the nephewâs dying gasp about the floor. He was trying to tell the servants what had happened.â

âTheâthe floor! Itâs going up!â Frank cried excitedly. âInto the tunnelâfast!â

The boys leaped out through the tunnel doorway and began making their way along the brick-walled passage to the summerhouse outlet. Frank was in the lead. They had gone about two-thirds of the way when he halted suddenly.

âHold it, Joe!â Frank whispered. âMaybe this way out isnât so smart after all!â

âHow come?â

âStrang knows now that we got into the house through the tunnel.â

Joe gave a low groan. âWhich means there may be a guard posted near the tiled floor!â

He mulled over the possibilities. âBoy, we wouldnât have a chance to spot anybody in the dark, either. Unless we used our flashlightsâwhich would give us away!â

The boys quickly decided the risk was too great.

âI vote we try sneaking back up the basement stairs and see if we can talk Professor Darrow into helping us,â Frank said.

âHe was the one who gave us away in the first place,â Joe objected. âAnd he shouted to Strang that you had escaped from the lab.â

âI know, but weâd given him quite a surprise,â Frank argued. âThe way he looked coming up the stairs after hearing what Makin saidâwell, I have a hunch heâs been doing a lot of thinking.â

âI guess we have no choice,â Joe said. Suddenly his eyes narrowed. âSay, Frank! Take a look at that brick your lightâs shining onâthe one thatâs a little darker than the others.â

âWhat about it?â

âLooks to me as if the mortar is loose around it,â Joe said tensely. âDidnât Nyland tell us that Old Man Perth boasted the partnership papers were stashed outside the mansionâin a place that anyone could get at?â

Frank gave his brother an excited look. âGive me your jackknife, Joe!â

The knife blade passed easily around all sides of the loose brick. In a moment Frank had removed it. Behind the space where the brick had been was a deep recess. It was crammed with papers and small cloth pouches!

Frank fished them out, one by one. The pouches contained a dazzling assortment of gems, cut and uncutâdiamonds, emeralds, rubies, sapphires.

There were also stock certificates, bonds, and papers relating to various business deals. Among the latter was the partnership agreement between Perth and Karl Nyland, and a map of the lode site, signed with Nylandâs name.

âWow!â Joe muttered. âDo you suppose those jewels were Old Man Perthâs and did Strang locate this cache, as Karl Nyland Jr. thinks?â

âNylandâs right. Strang found it and heâs also using the tunnel as a place to hide his loot till the heatâs off. One of those bags of diamonds is labeled for delivery to Paul Tiffman.â

âThis would also explain about Karl Nylandâs amethystsâthe ones his father brought to Perth,â Joe reasoned. âStrang found them here and decided to peddle them, since they werenât âhot.â But Makin stole them from the glove compartment of Strangâs car.â

The boys crammed their pockets with part of the loot, and stuffed the rest inside their shirts. They also took the partnership papers. Then they headed back through the tunnel to the basement.

The house was quiet. Frank and Joe wondered if the men were searching the grounds. The boys tiptoed up the back stairway to the top floor, then made their way down the corridor to the laboratory.

Professor Darrow was seated at his workbench, holding his head in his hands. He looked up with a start as the boys entered. His face was drawn and pale. To the Hardysâ relief, he showed no sign of hostility, and made no effort to call for help.

âAre you really Fenton Hardyâs sons?â he asked, then brushed aside the boysâ attempt to show him identification from their wallets. âNever mindâpapers of any kind can be forged. The important thing is, I believe now that you and not Strang are telling me the truth.â

âI suppose what Duke Makin said convinced you,â Frank said quietly.

Darrow nodded listlessly. âIâve been a terrible fool. Strang led me to believe that he would finance my work for the public good. Instead, he was only interested in using my paralyzing-ray device to commit crimes.â

âIf you need any other proof,â Frank said, âwe found where he had hidden the loot from his jewel thefts, and we have it all right here.â

âThe main thing now,â Joe said, âis to call Dad and the police. Can I use that phone over there?â

Again Darrow nodded. âDo so, by all means.â

Joe lifted the telephone from its cradle and started to dial. Suddenly a cold, menacing laugh came over the receiver and the line went dead!

CHAPTER XX

Trapped!

JOE hung up with a gasp of dismay and turned to Frank. âSomeone just broke in and cut me off!â he exclaimed. âIt sounded like Strang!â

âWould Strang know what room the call was coming from?â Frank asked the professor.

Darrow looked at the boys unhappily. âYes. My phone line evidently is tappedâperhaps a signal device warns Strang when I lift the receiver. Sometimes when Iâd attempt to make an outside call, he would cut me off. His excuse was that he was keeping me safe from detection by foreign spies.â

âCome on!â Joe broke in. âRun for it!â

Darrow made no effort to escape, but the Hardys darted down the corridor toward the back stairs. Strang, Barney, and another henchman already were on their way up. Frank and Joe fled toward the front of the mansion, only to find Hirff and two others dashing up the front stairs.

âInto the lab!â Frank urged. âWeâll try the windowâmaybe we can slide down the drain-pipe!â

The boys hastily retreated to the laboratory. They were just flinging up the window sash when the criminals burst through the door and aimed two small, portable ray guns at them.

âHold it or weâll freeze you stiffer than iced mackerels!â Strang shouted as the boys turned to confront their captors. âThese little rods weâre holding are miniature models of that fancy gadget the prof used on you before. Weâve found them extremely handy on jewel heists.â

âPlease!â Darrow protested weakly. âThese boys have done you no harm. Let them go. Perhaps theyâll agree not to turn you in.â

âShut up, you sap!â Strangâs voice cracked like a whiplash. âYouâre in this as deep as any of us! Do you think we can let these kids go now, knowing all about our racket?â

Darrow shrank back as Strang proceeded to jeer at him.

âI conned you from the start, you egghead! Did you really think Iâd sink good money into this setup just so you could develop these blackout guns for national defense? And you swallowed all that junk about spies.

âWhat you were really doing here, Darrow, was getting us ready for the biggest jewel-theft operation in history. Those purple tear-gas grenades you cooked up were an extra bonus!â

Strangâs henchmen roared with laughter. Their response spurred him to greater boasting and he answered Frankâs and Joeâs questions freely. The first hint that the Hardys might be on his trail had come when the boys had followed him in his car.

The ghostly screams had warned the gang that someone was prowling near their tunnel exit, so next morning they had camouflaged the tiled floor with sod and brush. In doing so, they had found the jackknife bearing Frankâs name. Then later, one of the men had used the exit and had left the tiles uncovered. When Strang had found Frankâs pocketknife, he thought the Hardys had seen the floor.

Knowing from newspaper accounts of their earlier cases that the boys owned a boat, Strang had ordered two of his men to sabotage it. âI figured then it was time to scare you punks off or get rid of you for good,â Strang went on. The brothers had escaped with their livesâbut later, when the Napoli had happened to anchor near the Seacat, one of the gang, known as Moose, had attacked Joe in the bay.

As the Hardys had suspected, Strang had sent two of his men, Kelso and Trigger, to Chicago to pull the Spyker robbery, after telephoning a false clue to Mr. Hardy.

Strang had arranged to be aboard the chartered plane at the time of the robbery, in order to establish an alibi in case he was charged with the theft. He had arrived in Chicago in time to organize the transfer of the loot, stowing it in a secret compartment of Hirffâs plane and later taking it to the Perth mansion hideout.

Kelso and Trigger had gone to Gary, Indiana, to plant the decoy getaway car, then returned to Bayport by commercial airliner.

âHow did Makin happen to be at the airport the night of the robbery?â Frank asked.

âHe trailed Waxie, who was waiting for me to fly in from Chicago. But he didnât wait long before Makin jumped him, and made him unlock Hirffâs hangar so he could search it.

âThen he took Waxie back to the car and found the amethysts in the glove compartment. He knocked Waxie out and was going to leave him there, unconscious, as a warning that we should cut him in. But when you kids and that private eye showed up and spotted him, Makin took off. And when I came in, I had to leave the loot in Hirffâs plane and take a taxi back to the mansion.â

The gang had rented the cabin at Tigersâ Bight as an emergency hideout, intending to flee there in their cruiser if the police should close in. Jack Wayne had been taken there by Barney after he had contacted the Seacat by radio.

âWhat were you planning to do with Jack?â Joe asked.

âHe told Hirff your dad owed him money and wouldnât pay upâso now he was sore at you Hardys and looking for some quick dough. We thought if he was telling the truth, he might tell us how much you knew. If not, weâd get rid of him fast. Barney was keeping him at the cabin till I got a chance to question him.â

After Joe had photographed the chart found in Hirffâs plane, Hirff had phoned the news to Strang, and the gang had tried to snatch the film. When that move failed, Strang had radioed Barney to booby-trap the cabin and take off in Skyhappy Sal before the Hardys could get there.

On the Haley Building job, Kelso had learned about the delivery from a stooge in the jewelry company. Kelso had entered the building during business hours and had hidden in a washroom. Later, he had let Waxie in by the fire-escape door.

The two had sneaked downstairs to the lobby, where the watchman had been seated at his desk with his back to the stairway. They had blasted him with the ray gun.

Kelso then had tampered with the elevator and Waxie had installed duplicate fifth-floor numbers and name plates on the sixth-floor offices. Kelso had posed as Paul Tiffman to receive the diamonds from the messenger. The robbery accomplished, they had again blacked out the watchman and removed all traces of their ruse.

âHow did Makin learn you were planning to pull the job?â Frank asked.

Strang chuckled. âWe squeezed that out of him before we blacked him out. He was watching the mansion that day and trailed Kelso to the building. When Kelso never came out, he figured we were planning to pull a job there.â

âHow about that voice I heard over your tunnel intercom?â Joe put in, to keep Strang talking.

The jewel thief laughed. âPretty fast thinking on your part, kidâIâll hand you that much. Trigger thought Waxie had forgotten his orders and was calling for a quick fill-in.â

âGood thing I realized the guy on the line wasnât Waxie,â Trigger said. âHeâs a nut! Crazy about the gadgets in this place. Calling on the intercom. Pushing the floor release in that rigged-up room.â

âMaybe Waxie forgot to put the floor back in place the night we first saw it through the window,â Frank suggested, still playing for time.

âWaxie forgot once too often,â Strang grunted. âLast time, I about broke a leg. Got fed up. Lucky for Waxie he scrammed when he did.â

Meanwhile, Professor Darrow had furtively plugged in his blackout invention. Suddenly he snatched it up and aimed the machine at the thieves. But Trigger saw the maneuver.

âLook out, boss!â the gangster yelled, whipping out his own ray gun to fire.

Strang jumped clear in the nick of time. But Trigger had no chance to use his own gun. The blaze of brilliance from the professorâs machine paralyzed all five of Strangâs henchmen.

Strangâs own leap had left him momentarily off balance. The Hardys seized their chance. Frank stunned the gang boss with a hard right to the jaw. Joe wrested away his blackout gun, and in a few moments the two young sleuths had punched Strang into submission.

âIt would be safer, if I blacked him out,â Professor Darrow suggested to the boys. âThe rays from my device do no permanent damage. They simply affect certain brain centers and temporarily immobilize the subject until the neural circuits have time to clear themselves.â

âMaybe he has a point there,â Joe remarked to Frank with a grin. âWe have no handcuffs.â

As the professor was blacking out Strang, Frank spotted car headlights through the trees surrounding the mansion. A short time later Fenton Hardy, Chief Collig, and a squad of police rushed into the house to take over. They stared in amazement when they saw the helpless members of the gang.

âLooks as though we missed the preliminaries and the main event,â the tall investigator remarked to Collig with a chuckle. âTheyâre all out cold.â

The chief and his men grinned in satisfaction. âIâd say six KOâs are enough of a show for any evening!â Collig quipped.

âSeven.â Joe grinned. âI think youâll find another KO in the âguest room.â â

After hearing the whole story, Mr. Hardy and the chief were warm in their praise of Frank and Joe. But the boys pointed out that it was Professor Darrow who had brought victory at the last moment.

âIâm afraid youâve been badly misled, Professor,â Mr. Hardy said. âSome facts you may not know are these: Strang and his men had their eye on the Perth mansion as a hideout. When you bought it, they arranged to move in with you and used the ray gun as an excuse.â

Frank added, âAnd Makin, in trying to worm his way into the gang, offered to rent the place. He only wanted to find out if Strangâs group were just helping themselves to the mansion.â

Mr. Hardy went on, âBut, Professor, you certainly turned the tables on the gang! Iâm reasonably sure that any charges against you, for your part in Strangâs operation, will be dropped.â

âHow did you happen to get here, Dad?â Frank asked as the police were removing the prisoners.

âAfter I heard Tony and Chetâs story, and you two failed to return, I decided it was time to blow the whistle on this setup at the mansion,â Fenton Hardy replied, throwing an arm around each of his boys.

âWhat Iâd like to know is who rigged all those spooky alarm devices,â Joe spoke up.

Professor Darrow gave a wan smile. âI did, partly to keep off intruders and partly for my own amusement,â he explained. âIt was while I was wiring them into the mansionâs electrical system that I stumbled on the bedroom-studyâs disappearing floor and told Strang about it.â

Next day the stolen, rented motorboat was located, and the Hardys went to the hospital to see Jack Wayne, who had regained consciousness and was rapidly recovering.

âSo youâve wrapped up the case, eh?â the pilot said.

âFrank and Joe have,â Mr. Hardy answered. âBut we all feel bad about the loss of Skyhappy Sal.â

Jack grinned. âDonât worry. She was insured, so Iâll have a new Sal pretty soon.â

âDad says thereâll be a good bit of reward money,â Frank put in, âand youâll get half, Jack. That should buy your new Sal a lot of fancy trimmings.â

âWeâre still curious about that interrupted radio message of yours, Jack,â said Joe. âHow about spelling the whole message out for us?â

Jack thought for a moment, then asked for pencil and paper and wrote down the message as nearly as he could remember it. The boys bracketed the words which had been lost in transmission. The result read:

[IâM FLYING DOWN TO TIGERSâ BIGHT TO SEE A GUY HIRFF TOLD ME ABOUT. HE SAYS THAT] IF THE TIGERSâ BIGHT [SETUP CAN USE A PILOT, I COULD MAKE A LOT OF DOUGH. IâM TO USE THE CODE NAME] AMETHYST [TO IDENTIFY MYSELF].

A few days later the stones Makin had stolen were recovered, and an expert survey of the amethyst location showed that the lode, while not highly valuable as a source of ornamental gems, was worth developing for commercial purposes. The story was repeated at the Morton farm to Tony and Chet.

âThatâs a break for Nyland,â Frank commented. âJoe and I had decided to use part of our share of the reward money to pay his wifeâs hospital billsâbut nowââ

âMy shareâs going to help my folks buy a new car,â said Tony.

âYou guys have no imagination,â Chet retorted.

âListen, Chet, how about using your part to buy some detective equipment so you can help Frank and me on our next case?â Joe teased, not knowing that they would soon be called on to solve THE MYSTERY OF THE FLYING EXPRESS.

âOh yes?â Chet retorted. âHop over to the Bayport Soda Shop with me, and Iâll show you what Iâm investing inâa yearâs supply of the biggest banana splits you ever saw!â