The Great Airport Mystery

Valuable electronic parts containing platinum are being stolen from shipments made by Stanwide Mining Equipment Companyâ€™s cargo planes, and Frank and Joe Hardy are called upon to assist their world-renowned detective father solve the baffling case.

At Stanwide the boys pose as employees, and become suspicious of their bossâ€™s hostility toward them. Is he involved in the racket? And what is the truth behind the plane crash at sea in which Clint Hill, chief pilot for Stanwide, was killed?

Frank and Joe launch an aerial search for clues to the platinum thievesâ€™ hideout, believing that they will also uncover the mystery behind Hillâ€™s accident. The puzzling trail of clues leads the young sleuths to an uninhabited Caribbean island, near the scene of the plane crashâ€”then to a mountaintop in Montana and a danger-filled show-down with the band of thieves. But the final discoveryâ€”and most startling and exciting revelation of allâ€”is made in the boysâ€™ home town of Bayport.

Franklin W. Dixon fans will find suspense, action, and many breath-taking flying episodes in this thrilling story.

âThose ropes will snap any minute!â Frank thought fearfully

Copyright Â© 1993, 1965, 1957, 1930 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 : 978-1-101-07624-8

2007 Printing

http://us.penguingroup.com

CHAPTER I

Mysterious Flare

âToo bad we lost so much time fixing that flat, Joe. Dad wanted us home in a hurry to start work on a case.â

Frank Hardy speeded up the brothersâ convertible.

Joe studied a road map. âWeâre coming to a turnoff that could save us thirty miles,â he said. âLetâs try it.â

The boys kept a sharp lookout in the gathering dusk. Presently Frank slowed and spun the wheel. The entrance to the turnoff was narrow and flanked by heavy trees and brush. If they had not been watching for it, they could easily have missed it.

A second later Frank slammed on the brakes. The glare of their headlights showed a wooden barrier several yards ahead.

âOh, no! A roadblock!â Joe groaned.

âThatâs strange,â Frank murmured. âThereâs no sign to explain why the roadâs cut off.â

âMaybe itâs only for minor repairs,â Joe said hopefully. âLetâs take a chance.â He jumped out to move the wood barrier.

âOkay, but keep your fingers crossed,â Frank said. âIâd sure hate to get stuck in some pothole and break an axleâespecially at this time of night.â

Joe, blond and a year younger than dark-haired, eighteen-year-old Frank, dragged the barrier aside. Frank drove past, then Joe replaced the roadblock to its original position.

Climbing into the convertible again, he asked, âAny idea what this new case Dadâs working on is about?â

âNo, but the way he sounded, it must be urgent.â

Fenton Hardy, the boysâ father, was a former crack detective of the New York City Police Department. After retiring from the force to the waterfront town of Bayport, he had become a famous private investigator.

Frank and Joe, who seemed to have inherited their fatherâs sleuthing talents, often aided him in his investigations. The brothers had also solved several cases largely on their own, beginning with The Tower Treasure, and, most recently, the strange Mystery of Cabin Island.

Now a summer vacation trip had been cut short by the upcoming assignment. The boys continued their journey in the deepening darkness. Ahead, the road wound through isolated, hilly country. Here and there they encountered patches of light radiation fog, a phenomenon common to this type of terrain. After several minutes the Hardys were puzzled not to see any road construction, or any other reason for the barrier they had encountered.

âMaybe the roadblock was just somebodyâs idea of a joke,â said Joe.

Frank was about to answer when suddenly the brothers were startled to see an intensely bright red glow appear on the road ahead. Temporarily blinded by the light, Frank jammed on the brakes. The car skidded crazily, then came to a halt up on the side of a steep embankment that bordered the road.

âWhatâs that?â Joe shouted.

âLooks like a flare!â Frank answered, turning off the ignition.

The boysâ eyes became accustomed to the bright light just in time to spot a man scurrying off the road and into the woods. The stranger vanished quickly, but not fast enough to prevent the Hardys from getting a glimpse of his face. A split second later they heard a series of loud cracking sounds.

âThose are rifle shots!â Joe yelled. âBut where are they coming from?â

âThe woods. And they may be aimed at us! This car is too good a target. Weâd better get out pronto!â

But before either of the boys could move, a new sound captured their attention. The mounting, throaty drone was unmistakable.

âThatâs an airplane coming down!â Frank cried out.

âAnd itâs headed this way!â Joe yelled.

At that moment the boys saw two bright lights approaching obliquely from the right and very low. Frank and Joe were able to make out its silhouette against the night sky, even through the glow of the flare. The plane had two engines and a sleek, streamlined fuselage that terminated at the rear in a high, swept-back tail section. Its landing gear was fully extended.

âThat pilotâs trying to set her down here!â Frank declared as he stared in disbelief.

âHeâs so low his wheels wonât clear the top of our car! Get down!â Joe yelled frantically.

No sooner had the brothers dived to the floor of the car than the plane passed overhead with an earsplitting roar. Its left wheel grazed the roof of the car. Already tilted on the embankment, the convertible toppled over with a smash. The Hardys blacked out.

Several minutes passed before either of them regained consciousness. Frank was the first to move. With great effort he and Joe managed to push themselves to an upright position.

âGet down!â Joe yelled

âYou all right?â Frank asked weakly.

âI feel as if Iâd taken a ride inside a cement mixer.â Joe groaned.

As their heads cleared, the brothers realized that the car was lying on its side. They forced open the door on Joeâs side and scrambled onto the road, then glanced about them. The flare was gone, and the woods remained dark and silent. As far as they could tell, there was no sign of the airplane.

Frank bent down, and with his pocket flashlight, examined a deep crease across the roof of the overturned car. âItâs from the wheel that turned us over,â he commented.

âWhat was that idiot pilot doing?â Joe snapped.

âI donât know,â Frank answered. âIf he was trying to make a forced landing, he would have crashed into the trees on the other side of the road. Yet thereâs not a trace of any wreck.â

âIt vanished just like everything else,â Joe said. âThe flare, the man who ran into the woods as we drove up, and whoever was using the rifle.â

âDid you get a look at the face of the man with the flare?â Frank queried.

âYes, but only for an instant,â Joe answered. âI think Iâve seen him some place before, though.â

âMe, too,â Frank agreed. âMaybe we saw a photo of him in Dadâs files. Letâs take a look when we get home.â

Except for several deep dents and scratches, the car did not appear to have suffered any serious damage. The boys decided to try rolling it back to an upright position.

âWeâll need a couple of long poles for leverage,â said Frank.

âMaybe we can find something in the woods,â Joe suggested.

The boys took a flashlight from the car and started into the wooded area. They searched the ground carefully for fallen trees to serve as poles. Suddenly they were startled by a sharp, snapping sound, like the breaking of a twig, behind them.

âDid you hear that?â Joe whispered.

âYes. Listen!â

There was a second snap. Then silence. The boys stared into the darkness, but could see nothing.

âProbably some animal,â Frank said.

âI guess so,â Joe agreed.

The Hardys were about to resume their search when the snapping of twigs was heard again. Frank switched off the flashlight. The boys listened. From nearby came the faint rustle of leaves. It was as if someone, or something, were approaching stealthily.

They turned and looked behind them. Suddenly the outline of a man appeared against the heavy brush. He seemed to be pointing something at them. Was he the man with the rifle? The Hardys stood frozen in their tracks.

CHAPTER II

Factory Detectives

âWHO are you?â Frank demanded. He snapped on his flashlight and directed the beam toward the mysterious figure. He was not the man who had set the flare.

âDrop that light!â the stranger ordered gruffly.

Frank tossed the flashlight to the ground. The man then played a bright light of his own on the Hardysâ faces and slowly stepped toward them. As he approached, the boys could see that he was armed with a double-barreled shotgun.

âWhat are you doing here?â he growled.

âOur car turned over,â Frank began, âand weâre looking forââ

âWhatâs that you say?â the man shouted, cocking an ear toward Frank. âSpeak louder!â

âI said our car turned over,â Frank shouted, âand we areââ

âYour car turned over?â the stranger interrupted. âHow did that happen?â

âThe wheel of an airplane struck the roof.â

âAirplane? What airplane? Speak louder!â

The stranger was apparently so hard of hearing he had not heard the noise. On the other hand, the boys wondered if he could be connected with the mysterious events that had occurred earlier and was bluffing. They decided to force the issue. Frank told him briefly about the roadblock, the red flare, and the low-flying plane. He also mentioned seeing a man run off the road into the woods, and said that later they had thought they were being shot at.

âYouâre both crazy,â the stranger sneered. âI didnât see any airplane or red flare.â

He then motioned with his flashlight for the boys to walk on past him. âYouâd better get out of here right now, if you know whatâs good for you! Youâre on private property!â

âWe didnât notice any fences or signs around here,â Joe retorted.

âI donât care what you didnât notice!â the man shouted. âGet going!â

As the boys walked past him, they managed to catch a closer glimpse of his face. They saw that he was middle-aged, and pale and haggard.

Frank asked that he and Joe be allowed to find a couple of poles. The stranger hesitated, then gave permission.

Frank and Joe soon located several fallen saplings. They picked two of the strongest and dragged them to the car. They then positioned the saplings under the convertible and pushed against them with all their strength. At first it seemed hopeless, but after another powerful lunge, the car began to move, then shivered to an upright position.

The brothers stopped for a moment to catch their breath. They noticed that the stranger was watching them from the edge of the woods.

âGet going!â he yelled angrily.

Frank tugged at the jammed door on the driverâs side. Finally it opened. The boys got in and Frank turned the ignition key. After a few seconds the engine came to life. Except for the draining off of some fuel and oil, the car seemed to be in safe-driving condition. Frank maneuvered it carefully for a few minutes, then gathered speed and set off for home.

âWow!â Joe sighed. âI like excitement, but tonight was enough to last me for a month.â

Trying to find some answers to all that had happened, the brothers discussed the mystery, but were unable to arrive at any conclusions. As they got closer to home, their thoughts shifted to the telephone call from their father. What could the case be? Their faces lit up in anticipation.

Nearly three hours later the boys reached Bayport, where they lived. As they entered the living room of the Hardy house, their mother greeted them. She was an attractive, slender woman, who tried to take the adventurous life of her family philosophically. Mrs. Hardy could not help worrying, however, over the dangers she knew they must encounter.

âHello, sons,â she said in a relieved voice.

âHello, Mother,â the boys answered, and Frank added, âSorry to be so long driving back, but we took a short cut that turned out to be time consuming.â

âMy goodness, what happened to you two?â she asked in alarm as they bent down to kiss her. She pulled them closer to a lamp. Joe had a large swelling near his temple, Frank an ugly bruise under his left eye.

Mrs. Hardy wanted to call the doctor, but the boys assured her that their injuries were not serious. In order not to upset her further, Frank said they had been bruised when he had stopped the car short.

Miss Gertrude Hardy, sister of the boysâ father, entered the room. She was a tall woman who secretly adored her nephews but constantly scolded them for not being cautious enough in their sleuthing. Occasionally her dire predictions of danger came true! At seeing their injuries, she immediately said, âIce packs for both of you!â

âPlease, Aunty, not until we talk to Dad,â Frank pleaded.

The brothers hurried to their fatherâs study. Mr. Hardy looked up as they entered.

âHello, boys,â he said. âGlad to see you back. Sorry I had to break up your visit.â Noticing their injuries, he asked, âWhat happened?â

Joe told Mr. Hardy about their adventure while Frank began to hunt through the identification files. Several minutes later he held up a card.

âI found it!â he exclaimed. âJoe, Iâm sure this is the man with the flare who ran into the woods!â

Joe looked at the photograph mounted on the card. âYouâre right!â

Frank handed the card to his father. Mr. Hardy took it and leaned back in his chair. He was a handsome, athletic-looking man.

âAh, yes,â he said. âI seem to remember this man. Heâs an ex-convict known only by the name of Bush Barneyâno aliases. He served a three-year term for robbery.â

âI wonder,â said Joe, âif thereâs some connection between Bush Barney and that airplane we saw. Could the pilot have been dropping stolen merchandise to him?â

âItâs a possibility,â Frank replied. He reached for the telephone and began dialing a number. âIâm going to check with the control tower at Bayport Airport to see if they know of any aircraft that is overdue.â

Frank identified himself to the tower operator on duty, then questioned him. He was told that all flight plans to and from Bayport had been properly closed. The tower operator also said that transient aircraft, as well as those permanently based on the field, had been accounted for. Frank hung up, disappointed that he had not uncovered a lead.

Meanwhile, Mr. Hardy had been jotting down a few notes on Bush Barney. âPerhaps,â he said, âthe incidents you have told me may be linked to a new case I have coming up. Thatâs why I asked you boys to come back.â

Mr. Hardy stated that earlier in the day he had received a visit from a Mr. Albert Allen, president of the Stanwide Mining Equipment Company. The plant was located on the north edge of Bayport Airport, and manufactured mechanical and electronic tools and other equipment for the mining industry.

Mr. Allen had told the detective he was certain he had unearthed a racket within his company. He had been getting complaints from customers about shortages in orders. In each instance, a typed note had been enclosed in the shipment promising that the shortage would be made up at a later date. But the promise had never been kept, the customers said, and they needed the material.

âWhat sort of material have the shortages involved?â Frank asked.

âMostly small, but expensive, components,â his father answered. âEspecially electronic parts with a high platinum content.â

Mr. Allen, the detective continued, had ordered an examination of the companyâs books. Everything had tallied.

Recently he had had a meeting with a Mr. Cosgrove, whose firm was one of Stanwideâs largest customers. Mr. Cosgrove had threatened to sever business relations with Stanwide because of the shortages. The publicity resulting from such a move could be extremely damaging to Stanwide, Mr. Hardy saidâeven more damaging than the loss in orders.

âIt sounds like an interesting case,â said Joe. âWhen do we begin?â

âTomorrow,â Mr. Hardy said. âFirst weâre going to stop at the doctorâs office and have him check those bruises of yours. Then weâll drive out to Stanwide to meet Mr. Allen. Iâm arranging to have you boys pose as company employees.â

âEmployees?â queried Frank.

âYes,â his father answered. âActually, you are going to be doing a factory investigation job.â

CHAPTER III

The Ghost Pilot

THE next morning, after the doctor had assured Mr. Hardy that the boys were fit, the detective and his two sons proceeded to the Stanwide Mining Equipment Company for a meeting with Mr. Allen. Soon they were being ushered into a spacious, paneled office.

A graying, distinguished-looking man arose from behind a desk and extended his hand in greeting. Mr. Hardy introduced Frank and Joe. After handshakes Mr. Allen gestured for all of them to take chairs.

The tall executive studied the boys for a moment, then glanced at Mr. Hardy. âIâve already made arrangements for your sons to be hired as summer employees of our firm.â

âGood,â Mr. Hardy answered. âIâm convinced that this is the only way the case will be solvedâby someone working on the inside.â

âOur posing as employees,â Frank spoke up, âwill allow Joe and me to investigate without anyone becoming suspicious.â

âI hate to think that any of my employees may be mixed up in this,â Mr. Allen said with a sigh. âHowever, Iâll do anything to help clear up the mystery.â

âDad tells us that most of the shortages are of parts that contain platinum,â Joe remarked.

âThatâs correct,â replied Mr. Allen. âItâs understandable, too, for they would be the most valuable.â

âWhere do you obtain your platinum?â Frank queried.

âWe purchase it in large quantities from a firm in Canada.â

As they discussed the case, Mr. Allen noticed the brothers glancing at a strange voodoo figurine mounted on the wall.

âI see you boys are interested in my little curio,â he said.

âYes, we are,â Frank admitted.

âThe figurine is more to me than just an ornament,â Mr. Allen said sadly. âIt is also a reminder of a tragedy that occurred several months ago.â

The Hardys listened intently as he related the story. His firm owned a subsidiary company known as Stanwide Research and Development Laboratories. Its function was to conduct exploratory mining work in various parts of the world.

Recently, an expedition had been sent in one of the firmâs aircraft to Ile de la Mer, a small uninhabited island far out in the Caribbean. During the return trip the plane had developed engine trouble and crashed into the sea. Only the copilot, Lance Peterson, had survived. The pilot, Clint Hill, and three mineralogists had gone down in the sinking aircraft. Lance Peterson was now chief pilot for the company.

âI considered Clint Hill not only a loyal employee,â said Mr. Allen, âbut also a close friend. It was Clint who sent me the figurine. I was shocked and grieved when he was lost.â

Mr. Allen sat silent for a few seconds, then came back to the case at hand.

âNow, about your employment,â he said to the boys. âYour father asked me to select jobs that would give you as much freedom to roam around the plant as possible. I think an assignment as plant messengers would fill the bill.â

âThatâs perfect,â Mr. Hardy agreed.

Mr. Allen asked the boys when they would like to start.

âHow about tomorrow?â Frank suggested. âThe sooner the better.â

Mr. Hardy informed his sons that right now he and Mr. Allen were going .to examine the firmâs employee files for possible suspects. He suggested that in the meantime Frank and Joe become acquainted with the layout of the plant.

Mr. Allen had one of his office clerks take the young detectives on a brief tour of Stanwide. Then they were introduced to Art Rodax, the man who was to be their boss. Rodax was heavy-set, with thinning hair and a sour-faced, belligerent expression. He seemed to develop an immediate dislike for the two new employees.

âFactory messengers, eh?â he blurted. âI donât need any more help.â

âBut weâve already been hired,â said Joe. âWe start tomorrow morning.â

âThen I guess thereâs nothing I can do about it,â Rodax growled. âBut let me catch you lying down on the job just once and you wonât last a day.â

He was still grumbling when the boys left to return to Mr. Allenâs office.

âBoy!â Joe exploded. âIâm sure glad we arenât really going to be working for that sourball.â

âMe too,â said Frank. âHeâd make a starving man lose his appetite!â

Mr. Hardy told the boys that his examination of the employee files would take longer than expected. Since Mr. Allen had offered to drive him home later, he suggested that his sons take the car and go now.

âWhen I get home Iâll let you know if I find out anything,â the detective promised.

âOkay, Dad,â said Frank. âJoe and I want to stop at the airport on the way back to double-check with Lou at the tower on all of last nightâs flights.â

Light rain was falling, and a heavy prefrontal fog was beginning to move in as the Hardys arrived at the field. They walked to the tower and climbed the winding steps to the top.

As they entered the control room, Lou Diamond, the tower chief, waved a greeting. A short, stocky, good-natured man, with crew-cut red hair, he nevertheless had an air of authority.

âYou boys picked a fine day to pay us a visit,â he said with a laugh. âIn a little while that fog will be so thick you can walk on it.â

The Hardys peered through the tinted panes of glass enclosing the control room. Already the ramp area immediately below was vanishing in a milky fog.

âWeâre not here just for a visit,â Frank announced. âWe thought you might help us by giving out some information.â

The young detectives then told the tower chief about their encounter with the low-flying aircraft the night before.

âWere you able to identify the type of aircraft, or get its registration number?â Diamond asked.

âIt was too dark for positive identification,â Joe replied. âAnyway, we were both busy ducking!â

Diamond looked thoughtful. âFunny. I know of no private landing fields in that area.â He paused. âThere have been several strange things going on in the air around here lately,â he said.

âWhat kind of strange things?â Frank asked.

âAt night weâve picked up messages between planes that must be in code. They sure make no sense.â

Suddenly a light flashed on the console and one of the radio speakers crackled to life. It was the unicom frequency used by flight students for practice and by pilots wishing to communicate with one another in the air.

âBayport tower! This is Highflite One-Four-Alfa!â the pilot identified his craft, using Alfa for A. âHow do you read?â

To the boysâ astonishment, the tower chiefâs normally ruddy face turned pale. He picked up a microphone, then stood motionless, apparently unable to speak. Finally, in a quivering voice, he responded:

âHigh ... Highflite One-Four-Alfa! This is Bayport tower. Reading you loud and clear.â

âThis is One-Four-Alfa. Not on an instrument flight plan. We are on top at thirteen thousand. Can you get us cleared for an ILS approach at Bayport?â

âNegative, One-Four-Alfa,â replied the tower chief. âBayport is now below ILS minimums. Advise you contact Air Traffic Control on the proper frequency.â

There was no answer from the aircraft. Diamond seemed to be under a great strain. He placed the microphone on a table and mopped perspiration from his face.

âWhatâs wrong?â Frank asked anxiously.

âThe aircraft that just called! That identification number!â the tower chief said in a shaky voice.

âWhat about the identification?â Joe urged.

âThatâs the number of the plane once owned by Stanwide Mining! The one that crashed in the sea several months ago!â

âM-m-m, that surely is strange,â Frank said, frowning.

âI donât know whatâs going on,â replied the tower chief. âBut Iâm sure of one thing. The pilot who called sounded exactly like Clint Hill!â

Just then the radio speaker again crackled to life. A weird sound, like a disembodied chuckle, came eerily from it. Then a voice spoke. âThe dead can tell no tales!â

âThat is Clint Hill!â Diamond murmured, looking like a ghost himself.

âWhat do you make of it?â Frank asked.

âOnly one thing,â said Diamond in a frightened voice. âI never used to believe in ghosts. But now I do!â

CHAPTER IV

Police Orders

FRANK and Joe, startled by the unearthly voice, were equally amazed by the tower chiefâs admission that he believed in ghosts!

âThere must be some other explanation,â Frank said.

âWell, maybe. I guess I lost my head for a moment. But thereâs no way we can check on the aircraft,â Diamond declared. âOur field doesnât have airport surveillance radar, and the pilot said he wasnât on an instrument flight plan, so Air Traffic Control wouldnât have any record on him.â

âYou are required to keep a record on tape of all two-way communications between the tower and aircraft, arenât you?â asked Frank.

âYes,â Diamond replied.

âCould it be arranged for us to borrow a copy of the tape with Hillâs voice on it?â

âIâll have to check with our regional office,â said the tower chief. âBut in view of the circumstances, Iâm sure it will be all right.â

The boys, puzzled by this airport mystery, left the control tower and headed for the terminal building.

âLetâs find a telephone and call Mr. Allen,â said Frank. âI want to tell him what happened, and also ask him where we can find Lance Peterson.â

Mr. Allen was astounded at hearing the news about Clint Hill. He was certain that it was someoneâs gruesome idea of a joke. Frank then asked him if he had heard anything about the strange coded messages that Lou Diamond had mentioned.

âNo, I havenât.â

Frank next inquired where he could find Lance Peterson, and was told that he should be in his office at the Stanwide hangar.

The Hardys walked along the north side of the Bayport field until they came to the Stanwide hangar. It was a huge metal and stone structure with a high convex roof. On each side of the building were lean-tos which housed the shops and offices of the companyâs flight operations. The door to one of these offices was marked CHIEF PILOT.

The Hardys knocked, then opened the door and walked in. Standing near a window was a man of average height, with sandy-colored hair and a hard, weathered face. He turned and stared at the Hardys as they entered.

âMr. Peterson?â asked Frank.

âThatâs right,â the man replied. âWhat can I do for you?â

The boys introduced themselves and announced that they would like to ask him a few questions. Peterson agreed, and appeared quite calm and pleasant until Frank asked him about the crash at sea in which Clint Hill had been lost. Petersonâs face paled. He nervously sat down behind his desk and clutched both sides of the chair.

âWe crashed, and thatâs all there is to it!â he snapped. âLetâs drop the subject.â

âWhat was the cause of the crash?â Joe asked.

âThe airplaneâs at the bottom of the ocean,â said the pilot. âThereâs no way I can check for the reasons.â

âYou were in the plane,â Frank countered. âCanât you make a guess?â

âBoth engines quit,â Peterson said. âIn those circumstances, fuel contamination is the most probable cause.â

âAre you certain Clint Hill is dead?â Joe queried.

âOf course he is!â Peterson answered impatiently. âWhy do you ask that?â

âBecause his ghost contacted the tower just a little while ago,â Frank announced.

âIâm not in the mood for bad jokes,â shouted the pilot, leaping to his feet. He glanced at his wrist watch. âAnyway, Iâm scheduled to fly in a few minutes. Iâll have to go.â

The boys left the office, with Peterson trailing close behind them. He pulled the door shut, locked it, then walked off without saying another word.

âWhat do you make of him?â Joe asked his brother.

âOur questions sure made him uneasy. If you ask me, heâs trying to cover up something.â

The young detectives decided to look around the hangar for possible clues to the mystery. They entered by a side door and acted very casual, as if interested only in seeing the aircraft stored there. They had covered nearly half the premises when a young man came strolling out of the pilotsâ lounge.

âHey, look!â said Joe. âThereâs Jerry Madden!â

The young pilot was a wiry, good-looking youth whose brother was a teammate of the Hardys on the schoolâs varsity football squad.

âHello, Jerry!â called Frank.

Jerry turned. When he saw the boys, who ran to meet him, his face broke into a wide smile.

âHi! What are you fellows doing out here at our lil ole aerodrome?â he asked with a laugh. âGetting the yen to do some aviating?â

âWeâd like nothing better than a short hop in a sightseeing plane,â Frank said with a grin, in an effort to explain their presence without arousing Jerryâs curiosity. âBut the weather has other ideas. So we decided just to roam around and look at the planes.â

âWhat are you doing here?â Joe asked Jerry.

âI have a job flying for the Stanwide company,â Jerry explained. âI was hired soon after I received my instruments and multiengine ratings last spring.â

As they talked, the boys were not aware that a uniformed policeman was approaching from behind. The officer hailed them.

âWhat are you fellows doing here?â he demanded.

âI work here, Officer,â Jerry said.

âAnd who are you two?â the policeman said, eying the Hardys carefully.

âTheyâre Frank andââ Jerry began.

âLet them speak for themselves,â interrupted the policeman.

âIâm Frank Hardy. This is my brother, Joe. Weâre going to work for Stanwide.â

âIâll have to see some identification.â

The boys extracted cards from their wallets and handed them to the policeman. He examined the cards, then suddenly became apologetic.

âI know of you and your father by reputation,â he said. âSorry to have bothered you.â

Suddenly Joe sensed that they were being watched. He glanced to his left, without turning his head, and out of the corner of his eye glimpsed a manâs face peering at them from behind an airplane near the entrance. But the face drew back out of sight before Joe could distinguish the features.

âAre you boys here on a case?â the policeman asked.

âWeâre on vacation. This is a summer job,â Joe replied, speaking more loudly than usual for the benefit of the man behind the plane. âWe were just looking at the companyâs airplanes.â He nudged Frank to agree.

âWhat seems to be the trouble, Officer?â Jerry questioned.

âOur desk sergeant received a call saying that two prowlers had been seen in this hangar,â the policeman explained.

âDo you know who made the call?â Frank asked.

âNo, it was anonymous.â

Joe glanced in the direction where he had seen the face. It did not reappear. He motioned Frank to keep talking, then darted to where he had spotted the eavesdropper. No one was there.

The young detective quietly moved in the direction he thought the stranger must have taken. Joe found it awkward trying to maneuver, unseen, around the closely packed aircraft. Suddenly he spotted a stocky man in mechanicâs clothes walking quickly toward Lance Petersonâs office. Joe hid behind the tail section of an aircraft and watched. Upon reaching Petersonâs door, the mechanic anxiously jiggled the knob. Finding it locked, he walked away and out of sight.

Joe returned to Frank and the others. He apologized for going off so abruptly. âThought I saw one of the real prowlers, but I must have been mistaken.â

âHow many mechanics do you have working here, Jerry?â Frank asked.

âEight,â he answered. âBut thereâs only one on duty in the hangar todayâMike Zimm. Why do you ask?â

âOh, Iâm just curious,â Frank said nonchalantly. âJoe, itâs time we started for home.â

The boys, accompanied by Jerry and the policeman, walked toward the door of the hangar. As they neared it, Frank and Joe noticed something that brought them to a stop. On the floor lay a splintered section of wooden board.

The boys thought it strange that a piece of debris like that should be left on a floor so spotlessly clean.

Apparently the policeman thought so too. He bent down and picked up the board. Under it was a set of footprints, embedded deeply in the concrete.

âI wonder whose they are,â said Frank.

Jerry Madden moved closer and gazed down at the floor.

âI know whose footprints they are,â he said. âClint Hillâs.â

CHAPTER V

Warehouse Crash

âCLINT Hillâs footprints!â Joe exclaimed. âHow do you know, Jerry?â

âThe head of our company, Mr. Allen, was very fond of Clint,â the pilot explained. âShortly before he was lost in a crash at sea, the hangar floor was resurfaced with new concrete. Mr. Allen, perhaps partly in fun, asked Clint to make the prints. I wasnât here at the time, but itâs a well-known story around the flight department.â

The Hardys studied the footprints carefully. They noticed that the instep of the right foot was narrower than that of the left.

The policeman, who had to get back to his regular duties, said good-by. Jerry watched his young detective friends as they continued their study of the prints.

âI saw something just before I met you fellows that perhaps I should tell you,â he said.

âWhatâs that?â Frank asked.

âA manâs arm reached in through the door and placed that board over the prints,â Jerry explained.

âThatâs funny,â Frank commented.

Jerry went on, âI didnât attach any importance to it at the time. In fact, Iâd forgotten about it until I saw how interested you were in those prints. Maybe the person is still around.â

The boys dashed outside the hangar, but saw no one.

âWeâve heard of Clint Hill a couple of times today,â Joe told Jerry, but did not explain further.

After requesting Jerry to keep his eyes open and report to the Hardys any unusual goings-on around the hangar, the brothers left for home. Both were quiet, pondering over all that had happened during their visit to the hangar. Why had Hillâs footprints been covered? Was it to make certain the boys would not see them? And who had reported the presence of two prowlers to the police? Then there was the mechanic, Mike Zimm. Had he been the man who had eavesdropped on their conversation? The case, the boys agreed, was becoming even more puzzling.

During supper they related their dayâs adventure to the family.

âMighty queer business,â Aunt Gertrude commented. âYou boys had better watch your step. I donât know what weâre coming to when a companyâs employees canât walk around its private hangar without someone setting the police on them!â

The boys and their parents smiled. They were used to Aunt Gertrudeâs outbursts. Frank and Joe assured her they would try to duck any danger.

The next morning, Thursday, the boys rose for an early breakfast, eager to start their work at the Stanwide factory. Dressed in light khaki work pants and shirts, and equipped with appetizing lunches prepared by their mother and Aunt Gertrude, they drove off to the plant.

Frank and Joe reported to their boss, Art Rodax, exactly on time. Apparently this was not good enough.

âI want all new workers in my department to be here twenty minutes early!â Rodax growled.

âIs that a company rule?â Joe asked in surprise.

âItâs my rule!â Rodax announced angrily. âBreak it just once and youâre out!â

He then thrust two large handfuls of work orders at Frank and Joe.

âYouâve got thirty minutes to deliver these and get back here!â he bellowed.

The boys moved quickly and just managed to return on time. Rodax appeared to be disappointed. He had underestimated the Hardysâ efficiency. To make their task harder, he gave them a number of other chores in addition to their regular duties.

That evening the brothers went to bed immediately after supper, completely exhausted. Their second day on the job did not differ much from the first. Frank and Joe noticed that other employees of the department were given little to do.

âGood thing the weekendâs coming up,â Joe grumbled. âThe way Rodax drives us, he could have had all the Cape Kennedy gantries finished in two weeks!â

âWhat bothers me most,â Frank complained, âis that weâre not getting much of an opportunity to investigate.â

Yet the boys did not want to report the situation to Mr. Allen. There would be little the executive could do to help, they thought, without arousing suspicion.

Monday the young detectives had an unexpected change in luck. Rodax was assigned for the day to another section of the factory to help supervise the installation of a new duplicating machine. Grateful to have comparative freedom, even if just for the short time, the boys divided the work orders assigned them.

âMeet me in the warehouse at lunch hour,â said Frank. âWe can compare notes then, and at the same time look around the building.â

âSee you there about twelve oâclock,â Joe answered as he picked up a bundle of the orders and started off on his rounds.

Both boys watched carefully for anything suspicious in each department they visited. Not a single clue was uncovered to the mystery of the disappearance of Stanwideâs platinum components.

A few minutes past noon Frank and Joe greeted each other in the firmâs large warehouse. It was divided into two main sections for incoming and outgoing shipments. Stacks of cardboard boxes and wooden crates towered almost to the ceiling. There were also several pieces of heavy machinery stored along one wall in a neat row.

The Hardys found a wooden crate and sat down side by side to eat their lunches. They glanced around to make sure there were no other workers about. The only sound was the steady hum of the warehouseâs ventilating system. As a precaution, the boys spoke in low voices.

âDid you have any luck?â Frank queried.

âI didnât come up with a single clue.â Joe sighed with disappointment.

âI didnât find anything, either,â Frank confessed.

He told Joe he had investigated the handling of shipments from beginning to end, even to checking the bills of lading to see if they had been tampered with. His examination had revealed nothing.

âWhoeverâs running this platinum racket is a slick operator,â Joe remarked.

Unheard by the boys over the hum of the ventilating system, an overhead hoist was being put into operation. It was only a short distance behind the two young detectives. A heavy piece of machinery was slowly lifted off the floor, then edged to a position directly above Frank and Joe.

Suddenly the boys were startled to hear the sharp, metallic snap of a release clutch. This was immediately followed by a deep whirling sound directly above them. Frank and Joe looked up instantly. A massive bulk of metal was plunging toward them!

The boys made a frantic leap and went tumbling across the floor. The hurtling object pulverized the crate on which they had been seated, and sent splinters of wood and metal in all directions.

âThat was close!â Joe exclaimed.

Frank said grimly, âSomeone did that on purpose!â

As the boys scrambled to their feet, a door slammed violently at the far end of the warehouse. The Hardys ran to the door and flung it open. No one was in sight. They hurried outside and were about to search the area when they were confronted by a company guard.

âHold it!â he ordered. âWhatâs going on here?â

âDid you see anyone run from the warehouse just now?â asked Frank.

âNo one but you two!â the guard retorted. âI thought I heard a loud crash inside the building. What happened?â

The boys told him of the incident, and added that immediately after the crash they had heard someone fleeing from the building.

The guard eyed them with suspicion. âWeâd better go inside and take a look.â

Frank and Joe were annoyed at being delayed but had no choice in the matter. The man herded them into the warehouse and peered down at the huge, twisted piece of machinery on the floor. It not only had crushed the wooden crate, but had embedded itself deep in the concrete floor.

âWhatâs the big idea of lying about this?â he thundered. âYou caused this accident, but youâre blaming it on someone else!â

âWe had nothing to do with it!â Joe protested angrily. âAnd besides, we might have been killed. We were sitting on that very crate.â

âOh, yeah?â the guard sneered.

Frank looked hard at the man. âWe demand to see Mr. Allen!â he said.

âThe head of the company?â the guard asked. âFine chance of that. Mr. Allenâs a busy man. He wouldnât have time to talk to a couple of kids.â

âI wouldnât be too sure of that!â Joe warned.

The massive bulk of metal plunged toward the boys

The guard was bewildered by the demand. He broke into a nervous grin.

âWe donât have to bother Mr. Allen,â he said. âSomebody might lose his job because of this. Besides, this equipment is being discarded. Letâs just forget the whole thing.â

The young detectives did not answer. They left the warehouse and returned to their jobs.

âThat guard certainly changed his attitude in a hurry when we asked to see Mr. Allen,â Joe remarked.

âPerhaps heâs afraid that heâd lose his own job for not keeping a closer eye on things,â Frank suggested. âAfter what happened, weâd better watch our step around here!â

After supper that evening Frank and Joe joined their father in his study. The boys told him about their narrow escape, and of their failure to uncover any clues.

âIâm sure our real reason for working at Stanwide is suspected,â said Frank.

Mr. Hardy agreed, and added, âAs long as you continue to work at Stanwide, the thieves will probably lie low and you wonât learn anything. Besides, itâs too dangerous for you there. Your close call in the warehouse sounds as if the thieves are already trying desperately to get rid of you.â

The sleuth advised his sons to report to Mr. Allen everything that had happened, then resign their jobs.

âWork on the case from the outside,â he advised. âIâll arrange to obtain a clearance for you at the airport, so you can roam around just like the regular personnel.â

Frank smiled. âThen weâll have lots of time to keep a close watch on Stanwideâs hangar.â

Joe nodded. âAnd also, Iâd like to investigate the wooded area where we saw Bush Barney. That mystery hasnât been solved.â

âGood idea,â Frank replied. âAnd letâs make our first look an over-all oneâfrom the air.â

CHAPTER VI

Aerial Mission

âTHE meterologist at the airport says it should be clear tomorrow,â Frank announced as he put down the telephone.

âIâll call Ace Air Service first thing in the morning and arrange to schedule an airplane,â said Mr. Hardy. âWhat time do you boys want to take off?â

âWe plan to photograph the wooded area with our aerial camera,â Frank answered. âIf we arrive there shortly after twelve oâclock, the sun will be almost directly overhead. There wonât be any shadows from trees and other objects.â

âGood thinking,â Mr. Hardy said approvingly. âYouâll be less likely to miss important details that might be hidden if there were shadows.â

The investigator said that, meanwhile, he would check into the ownership of the land.

âIf it is private property,â said Joe, âI doubt it belongs to that fellow who chased us.â

At that instant Aunt Gertrude entered the study, carrying a large tray of brownies and lemonade. She placed it on Mr. Hardyâs desk.

âIâm sure you can all forget about your new case long enough to have a snack,â she said in a cajoling voice.

âFrank and I have to watch what we eat,â Joe said jokingly. âWe donât want to get airsick tomorrow.â

âAirsick?â the tall woman exclaimed, her eyes opening wider. âMy word! So you boys intend to go flying around in a bouncy plane?â

âWeâre just going up to take some pictures of crooks,â said Frank, grinning.

âIsnât your detective work dangerous enough here on the ground?â Aunt Gertrude asked sharply.

Mr. Hardy reached out and patted his sister on the shoulder. âDoing detective work while flying isnât any more of a risk than it is while riding in a car,â he told her reassuringly.

But Miss Hardy was not convinced. âAt least in an automobileââshe sighedââyou can get out and walk if the motor stops!â Shaking her head, she left the study.

âBy the way,â said Mr. Hardy, âa fellow from the Bayport control tower delivered a small package for you boys this morning.â

He extracted a set of keys from his pocket, unlocked his desk drawer, and took out the package. Frank eagerly opened it while Joe went to fetch their tape recorder.

âThis,â Frank explained, âis the tape containing the conversation between the control tower and someone who sounds like Clint Hill. I thought if we listened to the recording several times, we might be able to identify the âghostâ with one of our suspects.â

At that moment a stout, cheerful-looking boy strolled into the study.

âHi, Chet!â The Hardys grinned at the new arrival.

Good-natured Chet Morton was one of Frank and Joeâs best pals. Although comfort-loving and not fond of danger, he was loyal and had often helped the brothers in solving mysteries.

âHi, everyone!â Chet responded. Spotting the tray of refreshments, he eyed them hungrily.

âYouâre just in time for a little snack,â said Frank, chuckling. Their friendâs large appetite was well known to all!

âThanks. I thought Iâd stop by and see what you and Joe are up to!â

Just then Joe returned with the recorder. Frank put the tape on the machine and snapped the âStartâ switch. Seconds later a ghostly voice issued from the speaker.

âWhat is that?â queried Chet with a look of genuine astonishment.

âYouâre listening to a ghost.â Joe grinned.

âGhost!â Chet replied scornfully. âThat caterwauling wouldnât even scare a nervous cat.â

They played the tape several times. Chet tried to imitate the eerie voice.

âThe dead can tell no tales!â said the tape.

âThe dead can tell no tales!â Chet repeated.

âThatâs a pretty good imitation.â Frank laughed. âMaybe you can get work haunting houses.â

The Hardys listened to the tape a few more times, but were unable to associate the âghostâ with any of the suspects they had encountered.

Chet, who by now had consumed most of the brownies, glanced at his watch and announced it was time for him to go home. As he left the study, the boys were amused to hear him mumbling, âThe dead can tell no tales!â

The next morning Frank and Joe drove to the Stanwide Mining Equipment Company. Mr. Allen welcomed them with a smile as they entered his office.

âHow has the case been coming?â he asked. âHave you managed to uncover any clues?â

âWe havenât found much to go on,â Frank said regretfully.

The boys told him about their visit to the Stanwide hangar, and described all that had happened during their masquerade as employees. Mr. Allen expressed deep concern over their narrow escape in the warehouse.

The Hardys said they were certain that, somehow, information had leaked out as to their real reasons for working in the plant. He agreed that it might be too dangerous for them to continue their undercover work there.

âIâm disturbed to hear about Art Rodaxâs conduct,â Mr. Allen declared. âI wonât have a man of his character working for my company!â

âI suggest you say nothing to him,â Frank urged. âEvery one of your employees is a suspect at present. If Rodax is fired, it may spoil our chances of getting to the bottom of the platinum thefts.â

Frank also pointed out that it would be unwise for Joe and himself to resign suddenly from their jobs. This might make it appear that their investigation had uncovered some clues and would put whoever was involved in the thefts doubly on guard.

âThen what will you do?â Mr. Allen asked.

âWeâll get ourselves fired,â said Frank.

âHow?â his brother questioned.

âFrom the beginning, Rodax has resented our being hired,â Frank said. âMaybe itâs because heâs mixed up in the racket, and he knows about us. Anyhow, Iâm willing to bet he wouldnât need much of an excuse to fire us.â

Frank glanced at his wrist watch. âYou know how fussy he is about having us report for work twenty minutes early. Well, weâre now nearly an hour late. That should do it.â

After telling Mr. Allen that they would keep him posted on any new developments in the case, the young detectives went off to the messenger department. When they came face to face with Rodax, Frank could see that his plan was working out even better than he had expected.

âDo you know what time it is!â shouted Rodax. Although he seemed furious, the boys could sense that he was actually pleased with the situation.

âWe couldnât get here any earlier,â said Joe.

âYou wonât have to worry about that any more!â Rodax bellowed. âYouâre fired!â

The boys pretended to be angry and concerned. âWeâll report this to the main office!â Frank blazed.

âGo ahead!â Rodax yelled. âSee how far that will get you!â He turned and stalked off with a self-satisfied air.

The boys left the factory and started for the airfield. On the way they discussed Rodax briefly.

âI wonder how pleased old sour face would be,â Joe remarked, âif he realized heâd played right into our hands!â

A few minutes later the Hardys were walking toward a small frame building. A sign reading âAce Air Serviceâ spanned its entire width along the roof. Another, smaller sign, âOffice & Operations,â hung above the doorway. On the aircraft parking ramp the boys saw three single-engine and two multiengine aircraft bearing the firmâs name. As they entered the building, a voice called to them:

âFrank and Joe Hardy?â

The boys turned to see a tall, lean man walking toward them. He wore a tan cloth jacket and sunglasses with green-tinted lenses. He extended his hand in greeting.

âIâm Randy Watson,â he said. âI fly for Ace Air Service. I have a plane all set.â The pilot added he had often flown their father on trips. âIâve heard a lot about you fellows,â he added, smiling. âAre you on a case, or just going on a sightseeing ride?â

Before answering, Frank walked over to a large aeronautical chart attached to the wall. With his finger he circled an area, colored in shades of light green and brown, northwest of Bayport.

âWe want to take some aerial photographs in this locale,â he said. âJoe and I are sure we spotted an ex-convict there. Weâre curious to know what heâs up to.â

Randy stepped close to the chart and estimated the distance between Bayport and the area Frank had indicated.

âThatâs not far by air,â he observed. âWe can use one of the single-engine ships.â

âWeâd like to reach the area about noon,â said Frank.

The pilot checked his wrist watch. âThat means weâll have to take off within the next ten or fifteen minutes.â

Joe hurried to the airport restaurant to order sandwiches and milk for their lunch, while Frank returned to the brothersâ car to pick up the aerial camera and films. The boys reached the flight line just as Randy was completing a preflight check of the aircraft. In a few minutes they were strapped in their seats and taxiing toward the active runway.

The pilot remarked, âBecause of the direction of the wind, that runway is the only one I can use to head the plane into the wind.â

He tuned his radio to the proper frequency and contacted Bayport tower. An immediate reply crackled from the planeâs receiver.

âAce Service Flight Two-Six is cleared to runway One-Niner. Windâs from the southeast at fifteen knots. Altimeter setting, Two-Niner-Eight-Six.â

Randy paused to check his instruments, controls, and engine magnetos. The tower then cleared him for immediate take-off. Turning into the runway, he eased the throttle ahead. Soon he and his passengers were airborne and taking a course to the northwest.

The boys gazed down at the earth below. The terrain became more hilly with each passing mile. The expanses of wooded areas looked like rumpled deep-green carpet. Here and there, lakes and small streams reflected the sun in bright flashes almost blinding in their intensity.

The pilot adjusted his course, checked his watch against the small clock mounted on the instrument panel, then said to Frank and Joe, âWe should be coming up on the area youâre looking for in a few minutes.â

The Hardys scanned the surface below more intently. Far to the left, Frank saw a narrow ribbon of paved road that he surmised to be the highway from which he and Joe had turned onto the secondary road. Frank requested the pilot to fly closer to the highway.

âThere it is!â declared Joe. âThat must be the secondary road we drove along!â

Frank peered directly downward. The road itself was not visible, but a telltale cleft that snaked among the trees told him it was there. Randy banked steeply to the right and paralleled the road.

âCan we fly lower?â Frank asked.

Randy examined the terrain. âIt seems to be pretty desolate. I think we can drop to a lower altitude without breaking any air regulations.â

The pilot eased back on the power and allowed the nose of the airplane to drop a few degrees below the horizon. The large hand of the altimeter slowly moved counterclockwise, indicating a descent.

Randy leveled out at about five hundred feet, skillfully avoiding the hills. The cleft in the trees grew wider, bringing the road into view.

âLook!â Joe yelled. âThatâs where our car turned over. The saplings we used for leverage are still there!â

âStart taking pictures,â Frank ordered. âIâll keep an eye out for anything of special interest.â

Joe gripped the camera and pointed it downward. Randy banked the plane so the young detective could take more direct aim. Joe made several exposures as the pilot circled the area, gradually widening his turns.

âI just spotted something!â Frank shouted.

âWhat is it?â Joe readied the camera.

âIt looks like the roof of a small cabin,â Frank replied. âIf the sun werenât directly overhead, it would be hidden in the shadows. Itâs surrounded by trees and brush.â

âI see it!â exclaimed Joe. He focused the camera and released the shutter.

âThe cabin is near the spot where we saw Bush Barney,â Frank declared.

âDo you think he could be hiding out there?â Joe questioned.

âItâs possible. And perhaps our friend with the shotgun too!5â

The pilot rolled out of the turn. âWeâll fly straight and level for a few seconds,â he said. âIf we continue those tight turns for too long, we might get vertigo.â

Their straight course took them over an area on the opposite side of the road. Frank suddenly noticed a rectangular-shaped field that looked like a pasture.

âFly over that way,â he said to Randy, pointing almost directly ahead.

The pilot eased the plane into a course around the narrow clearing. Frank and Joe saw that the grassy field was bordered by trees and dense brush. At one end loomed a high, steep hill.

âWhat do you make of it?â Frank asked, glancing at the pilot. âDo you think a small plane could land there, and take off?â

âI doubt it,â Randy said. âBut letâs go down for a closer look-see.â

He dropped the planeâs nose steeply, pulling out over the clearing below tree level. He carefully dragged the field, then applied full power and turned sharply away from the steep hill ahead.

âThat clearing is only about nine hundred feet long,â he told the boys. âThe approaches are very bad. I doubt whether anyone could get a plane in there without rolling it up into a ball. And even if a landing were possible, heâd never be able to take off again.â

The boysâ thoughts turned back to the airplane they had encountered on the road. If it had crashed, where was the wreckage? It must have pulled up and gone off. Did the roadblock and the red flare have something to do with the maneuver ?

Frank took over with the camera. Quickly reloading it, he photographed the open area. Joe peered through his binoculars. Suddenly he snapped up in his seat.

âDown in the clearing!â he shouted. âSee those two men stalking along the edge!â

The pilot banked the plane and lined up for another low pass. As they approached, Frank also spotted the two figures. Joe focused his binoculars more sharply.

âIâm not sure,â he yelled excitedly, âbut I think one of those men is Bush Barney!â

As the plane roared closer, the two men whirled around. They glanced up, then turned and ran into the woods.

âQuick!â Frank shouted to Randy. âPull around and make another low pass!â

The pilot again pulled up steeply to turn away from the hill ahead. But just as he pushed the throttle forward for more power, the engine suddenly sputtered, then quit completely. Randy immediately dropped the nose in an effort to keep flying speed and avoid a stall.

The boys looked ahead. Through the windshield all they could see was a formidable array of trees, dense brush, and hills strewn with rocks and boulders. They tightened their seat belts and braced themselves for the worst. There was no place to land. They would have to crash!

CHAPTER VII

A Strange Request

RANDY Watson, his face grim, desperately switched fuel tanks. He pumped the throttle but the engine failed to react.

He put the plane into a gentle turn and headed down a narrow valley. The propeller slowly wind milled in the slipstream, as the anxious Hardys watched the ominous terrain rising steadily toward them.

The pilot continued to manipulate the fuel valves, mixture control, and throttle. Frank nervously glanced at the altimeter. They were rapidly losing altitude.

Finally Randy reached for a toggle switch marked âBooster Pumpâ and snapped it to the âOnâ position. He pumped the throttle vigorously. Suddenly the engine backfiredâonce, then twice. The boys held their breaths. There was a chugging sound for a few seconds! Then the engine roared to life.

Randy pushed the throttle to full power. Already the tops of trees were whipping against the plane, leaving green-colored streaks along the leading edges of the wings. The pilot eased back on the control stick and managed to pull away from the treetops. Ahead, he saw that the valley bent sharply to the right.

He banked the plane into a tight turn and followed the valleyâs course. It seemed to grow narrower second by second; the steep hills flanking each side squeezed closer. Randy checked the airspeed indicator, then raised the nose to gain altitude. Soon the hilltops were flashing by below them.

âWhew!â Joe exclaimed. âThat was too close for comfort.â

âWhat happened to the engine?â Frank asked the pilot.

âFuel-pump failure, I think,â Randy said. âRight now, weâre operating on the booster. Itâs acting as a kind of auxiliary pump, and should keep the engine running long enough to get us back to Bayport.â

During the return trip Frank removed the second roll of film from the camera, and placed it with the other one on the seat beside him. Eventually the airport came into view, and Randy radioed the control tower for a straight-in approach. The boys could see an emergency truck stationed near the runway as they touched down.

A small crowd had already collected on the parking ramp as they taxied in. One of the group was Jerry Madden.

âWhat happened?â he queried anxiously.

âThe pilot thinks it was fuel-pump failure,â Frank answered.

âI heard him declare an emergency on the radio in the hangar,â said Jerry. âWhen Lance Peterson heard you fellows were aboard, he asked to see you right away.â

âLance Peterson?â Frank said wonderingly. âHe wants to see Joe and me?â

The Hardys were so amazed at hearing Petersonâs request that they momentarily forgot about their photographing mission and near crash. They hurried immediately to the chief pilotâs office.

When the brothers arrived, Peterson greeted them with a smile. His attitude had apparently undergone a complete change since they had met the first time.

âI hear you boys had a pretty dose call,â he remarked.

âClose enough!â Frank responded tersely. He was eager to find out why Peterson had asked to see them.

The chief pilot looked haggard and worried. He sat down and nervously tapped the top of his desk with a pencil.

âI learned only recently that you two are amateur detectives,â he said.

âYes, we are,â Frank admitted. âBut what has that to do with your asking to see us?â

âI want you to take a case for me,â said Peterson. âPlease donât refuse.â

Frank and Joe were startled at the request. There was silence for a moment, then Frank spoke up. âWhat kind of case?â

Peterson spoke in a hushed voice. He repeated the story about the crash at sea in which Clint Hill had been lost.

âI was copilot on that trip, and the only survivor,â he said.

âWe know all that,â Joe said impatiently.

Petersonâs voice dropped almost to a whisper. The boys had difficulty hearing him.

âAs pilot in command,â he saidâalmost plead ingly, the boys thoughtââHill was responsible for the accident.â

Peterson grew even more tense. Perspiration began to show on his face.

âBut for some reasonââhe went on in a quavering voice, then paused as he got up and came to stand directly in front of the boysââClint Hill has started to haunt me!â

âHaunt you?â Frank exclaimed. âIn what way could a dead man haunt you?â

âClint used to whistle a lot,â said Peterson. âHis favorite tune was âHigh Journey.â Now I keep hearing him whistle itâhere, at home, over my plane radio. Sometimes he breaks off and laughs!â

âAre you sure somebody isnât just playing a joke on you?â Joe suggested.

âNo!â the pilot answered. âA few days ago I heard him radio the tower for landing instructions. Then he flew off, saying, âThe dead can tell no tales.â It all came in clearly on my office radio receiver over there,â he said, pointing to a box-shaped unit which stood on a table across the room. âI realize now you boys werenât joking.â

âThis is very unusual,â said Frank. âBut what can Joe and I do for you?â

âI know Iâm not hearing things,â Peterson stated. âSomebody is trying to drive me out of my mind, probably to get my job. I want you boys to find out who it is!â

âChasing ghosts is a bit out of our line,â Frank said. âWeâll have to think it over.â

Peterson appeared desperate. âI wish you would start on the case now,â he said. âBut if you must think it over, let me know as soon as you decide.â

The Hardys left Petersonâs office and started back to the Ace Air Service parking ramp. As they walked, the brothers discussed this new and puzzling development.

âIâd say he was off his rocker,â commented Joe, âif it werenât for the fact that we too heard the voice of Clint Hillâs ghost.â

âCould be,â said Frank. âBut I donât go along with Petersonâs idea that someone is trying to drive him out of his mind in order to get his job.â

Joe agreed and asked Frank if he thought they should take the case. Frank replied that it would be best to discuss the matter with their father before making any decision.

As they arrived at the parking ramp, the young sleuths saw Randy Watson standing near the airplane with a mechanic.

âFind the trouble?â Frank called.

âIt was the fuel pump that caused the engine to fail!â Randy replied.

âThanks to your skill,â Frank said with a smile, âwe avoided becoming a permanent part of the landscape!â

Randy said he hoped the trip had not been a waste of time.

âOh, no. We managed to get plenty of pictures before the engine quit,â Frank answered. âIncidentally, weâd better get the films developed just as soon as possible,â he said to Joe.

The young detectives climbed into the cabin of the plane. They were puzzled not to find the camera and containers of film where they had left them.

Frank shouted to Randy, who was standing on the ramp, âDid you take the camera and films into the operations building?â

âNo,â the pilot responded with a startled air. âAre you certain theyâre not in the cabin?â

The boys searched again, becoming more frantic with each second.

âWere you away from the plane at any time?â Frank asked Randy.

âOnly for a few minutes when I went to get a mechanic.â

The Hardys stared into the empty cabin.

âThose valuable pictures!â Frank burst out. âOur films! Theyâve been stolen!â

CHAPTER VIII

Masked Attacker

THERE was a moment of thunderstruck silence. Who had stolen the Hardysâ camera and films and why?

Randy was apologetic, saying he felt responsible for leaving the plane unattended. âIâll pay for the loss,â he declared.

âWe wouldnât consider it,â Frank said, shaking his head. âBesides, itâs not so much the camera weâre worried about.â

âThe films?â

âRight,â Joe added quickly. He cast a glance at his brother. âYou probably have the same suspicion I do, Frank. The thief might have wanted to prevent us from developing those pictures.â

âThen why did he take the camera too?â was Randyâs next query.

âBecause he figured there was more exposed film in it,â Frank explained.

âGood reasoning,â Randy agreed.

The boys recalled the small crowd that had collected on the ramp when their plane taxied in. Jerry Madden had been among them. Perhaps, Frank thought, he might know who some of the other onlookers were. The young detectives returned to the Stanwide hangar to question Jerry.

âI recognized only two faces in the crowd,â said Jerry, after the boys told him about the theft. âMike Zimm, the mechanic, and Aaron Lieber, a copilot mechanic, who seems to be a special pal of Lance Petersonâs.â

âZimm again.â Frankâs eyes narrowed. âOdd, the way he keeps popping up in our case.â

âSure is,â said Joe. âIâll bet that snoopy mechanic is somehow mixed up in the platinum business, but why would he want our films?â

The Hardys finally decided to trail Zimm and Lieber when the two men quit work for the day. Frank asked Jerry for a description of Lieber, then requested the pilot to check the menâs lockers for the stolen camera.

âThey keep them locked,â Jerry said. âEveryone around here does. But the doors have slats a little wider than is usual. Maybe I can peer in through the openings. Iâll try after Zimm and Lieber leave.â

The Hardys hurried from the hangar. Frank hid behind some engine crates a short distance away. Joe, at his brotherâs direction, went to the airport terminal building to telephone Chet Morton and another friend, Biff Hooper. Their palsâ help might come in handy if the Hardys ran into trouble while tailing Zimm and Lieber.

It was not long before Joe returned. âWeâre in luck,â he said. âChet can use his fatherâs produce delivery truck, which will be a good cover-up. Heâs starting for the airport immediately, and will pick up Biff on the way. I told Chet to wait for us near our car in the visitorsâ parking lot.â

Nearly half an hour passed before Zimm and a thin, bony-faced man with beady eyes emerged from the Stanwide hangar. âAaron Lieber,â muttered Frank. The young sleuths watched the men carefully. Neither of them carried anything, and the aerial camera was too bulky to be hidden beneath their coats. The pair stopped for a few minutes and talked in low tones, then got into separate cars and drove off.

Frank and Joe dashed to the visitorsâ parking lot. There they recognized the Mortonsâ farm truck and ran to it. Behind the wheel was the Hardysâ stout chum, and seated next to him, was tall, lanky Biff Hooper. Biff was an energetic boy, who prided himself on his boxing ability.

âThereâs no time to lose!â Frank declared. âJoe, you go with Chet in the truck and follow Lieber. Iâll take Biff with me in our car and tail Zimm!â

The two vehicles drove off and headed toward the airport exit, through which the two suspects would have had to pass. The boysâ timing was perfect. They neared the exit just as the cars driven by Zimm and Lieber pulled out onto the main road.

After driving a short distance, the two men took different routes. Frank followed Zimm, dropping behind as far as possible so as not to be conspicuous. Joe and Chet went in pursuit of Lieber.

As Frank and Biff rode along, Frank briefly outlined the situation to his friend, who nodded enthusiastically. âYou can count on me if thereâs any trouble.â He set his jaw and skillfully executed several left jabs in the air.

âSave your energy,â Frank told him with a grin. âYou might need it.â

The young sleuth kept his eyes fixed on the car ahead. As they entered town a short while later, he saw it slow down and stop. Zimm got out and went into a photographic shop. âFreemanâs Camera House,â Frank observed. He wondered if this was just a coincidence, or was Zimm planning to have the stolen films developed?

âWhen Zimm comes out,â he told Biff, âyou take the car and follow him. I want to question the shop owner.â

âBut when will we join up?â his friend asked.

Frank reached into his pocket and took out an emergency detective kit. From it he extracted a packet containing small pieces of vivid red paper, and handed it to Biff.

âAs you drive,â he told him, âdrop some of this paper every few seconds. That will leave a trail I can follow later.â

âBut what if I run out of paper?â Biff asked.

âIf you have to follow Zimm that far,â said Frank, âstay with him and find out where he goes. Then retrace your route. Iâll be following the trail on foot for as far as it takes me.

âIn the meantime,â Frank went on, âI want to call Jerry Madden at the Stanwide hangar and ask him if heâs had an opportunity to check the menâs lockers.â

Frank got out of the car. He found a public telephone across the street, where he was able to call and still keep an eye on the camera shop.

Summoned to the phone, Jerry Madden told Frank that he had found no sign of the aerial camera in either of the lockers. Frank requested Jerry to keep his eyes open and to call Mr. Hardy should anything turn up.

Frank had just completed the call when he saw Zimm come out of the shop and get into his car. He drove off, with Biff trailing behind.

Frank hurried into the camera shop. A man of medium height, with dark hair, was jotting notes in his order book. He proved to be the owner, Mr, Freeman.

The young detective identified himself, and asked if Mr. Zimm, who had just been there, had left film to be developed. Mr. Freeman said the man had left four rolls to be developed, but had given him the name R. C. Williams.

Frank realized that it was possible the films really did belong to a man named Williams, and that Zimm was merely having them developed for him. There would be no way of knowing until the pictures were developed.

âMr. Freeman,â said Frank, âwe Hardys are suspicious these are films that were stolen from us.â

The proprietor was eager to help the boys find out. He promised that when the negatives and prints were returned from the laboratory he would notify Frank immediately.

âThanks a lot,â Frank said, then left the shop. Daylight was beginning to fade, prompting him to hurry in search of the trail he had instructed Biff to mark. Almost immediately, he spotted the first bit of red paper. Then another piece, and another.

Frank estimated that he had walked nearly a mile when the trail led him onto a quiet residential street. He quickened his pace as darkness increased and a breeze sprang up, threatening to erase the paper trail. Dead ahead, he was suddenly elated to see his car parked on the street. As Frank neared it, he could see Biff at the wheel.

âHow did things work out?â Frank asked in a low voice, as he eased into the seat beside his pal.

âLuckily your suspect reached his destination before I ran out of paper,â Biff said.

He pointed to a house a short distance away and told Frank that Zimm was inside.

âHe lives there,â said Biff. âI got out and walked past the house. His name plate is posted on the lawn.â

Frank said that he wanted to watch the house a while. âBiff, how about your driving to the nearest store and picking up some sandwiches, milk, and ice cream for us? We may be here a long time.â

Biff went off and Frank stationed himself behind a tree. Daylight was now completely gone. The area was quiet, and light radiation fog was beginning to drift from the trees and shrubbery. Frank folded his arms against a chill that was developing in the air. He hoped that Biff would not be too long getting back.

Suddenly the stillness was disturbed by the sound of someone whistling. It seemed to be coming from the far side of Zimmâs house. Frank recognized the tune.

âHigh Journey!â

An eerie feeling gripped him. Was he hearing the ghost of Clint Hill?

The young detective bent low, crossed the street, and carefully edged toward the house. The sound, he was now certain, was coming from the far side of the dwelling. Frank slowly crept to the rear and listened. The whistle was louder now. He braced himself, then broke into a fast sprint.

As Frank rounded the corner of the house, he suddenly collided with a tall man. The force of the contact threw both of them to the ground. Dazed for a second, Frank took a deep breath, then scrambled to his feet.

The stranger also got up. He was wearing a mask! The man turned to run, but Frank was too fast for him. He managed to catch him by the collar. As the two tumbled and rolled across the ground, the stranger swung his fist.

Frank received a hard body blow that badly stunned him. The stranger leaped to his feet and ran. Frank made an effort to pursue him, but was too late. With consternation, he watched the masked figure vanish into the darkness.

CHAPTER IX

Alley Escape

MEANWHILE, Joe and Chet had followed Aaron Lieber to his apartment house. It was a small stone building with doors to the outside at both the front and rear.

They parked the truck half a block beyond it and hurried back. Joe quickly scrutinized the premises. Then he assigned Chet to guard the rear door, while he himself would watch the front.

âIf Lieber has our camera hidden in his apartment, he may sneak it out,â Joe told him, âso keep your eyes open.â

âOkay,â Chet answered. âSay, this kind of work sure can give a man an appetite,â he hinted.

Joe knew that once his chum had felt the pangs of hunger, it was hopeless to try taking his mind off food. It took little prompting to send Chet rushing off to get both of them something to eat.

The young detective watched both the front door and the service alley of the apartment house. No one came out, and it was not long before his stout pal reappeared carrying sandwiches, cartons of chocolate milk, and fruit.

He handed Joe an apple. âThis will do for an appetizer,â he announced.

Chet then divided the rest of the food and carried his portion down the narrow alleyway to take up his post at the rear door of the building.

Actually, Chet found two doors there. One was located at the top of a short iron stairway and led into the first floor of the apartment house.

The second, which obviously led to the basement, was situated directly below the other. Chet looked around and selected a vantage point in the shadow of an adjacent building.

âGuess nobody can see me here,â he thought.

As Chet began munching on his third sandwich, his eyes suddenly focused on the upper door. It was, he realized, being eased open. The figure of a man carrying a large package under his arm slowly emerged. Closing the door quietly behind him, he crept down the stairway.

âThe camera!â Chet decided.

He bolted from the shadow of the building. The man spotted him immediately. Startled, the stranger turned and broke into a fast run up the alleyway coward the street. Chet took off after him, still holding his sandwich and carton of chocolate milk.

The distance between Chet and the man he was pursuing rapidly closed. In desperation, the stranger stopped and whirled about. Chet was caught off guard.

âYouâyouâ!â the man hissed at him.

Holding the package with one hand, he reached out with the other and wrenched the carton of milk from Chetâs grasp. Then he threw its contents full force into the boyâs face!

âThatâll teach you!â the man snarled.

Chet was blinded by the deluge. He stood sputtering, vigorously wiping the liquid from his eyes. By the time he could see again, the man had disappeared.

In disgust Chet dashed out of the alleyway and around to the front entrance of the apartment house, to warn Joe. No one was there! The farm truck was gone.

Chet was in a quandary. Not only had the stranger disappeared, but so had Joe!

âPerhaps,â Chet thought, âJoe spotted the man running from the alley with the package and drove after him. I sure hope so.â

The stout boy took up a position across the street from the apartment house. From there, he could watch for Joe and guard the front of the building at the same time. The only people he saw come out were two women carrying small handbags. He observed nothing suspicious.

Finally Joe pulled up in the truck and hopped out. Chet ran to meet him. âI was beginning to worry,â said the plump boy. âWhere did you go?â

âThatâll teach you!â the man snarled

âWhile watching from here, I saw a man running out of the alley,â Joe answered. âHe was Lieber! Before I could catch him, he jumped into a car parked up the street. I chased him in your truck, but I got mixed up in a traffic jam and lost him.â

Chet told Joe about his encounter with Lieber, and pointed to his chocolate-stained clothes. He apologized for having been caught by surprise.

âIt couldnât be helped,â Joe excused him. âThe car that Lieber jumped into was waiting for him, Iâm sure. I managed to get the license plate number. We can check it out tomorrow with the motor vehicle department.â

By now the boys were convinced that there was little to be gained by continuing to watch the apartment house, so they decided to go home.

âWhat do you think Lieber was up to?â Chet asked as they rode through the Bayport streets.

âI donât know,â Joe responded. âBut whatever it was, he certainly wasnât wasting any time.â

âDo you think that was the camera he was carrying?â Chet questioned.

âYes. Some pal might have sneaked it from the airport to Lieberâs place. We have no proof, though.â

Chet stopped at the Hardy house and dropped Joe off. Then he sped for home, his face beaming with anticipation of the hearty meal he knew would be waiting for him.

Joe was about to enter the house when he saw Frank turn into the driveway. âHilâ he called.

âDid you just get back?â Frank asked as he climbed out of the convertible.

âYes. Did you have any luck following Zimm?â

âEnough to make me more suspicious of him,â Frank replied. âIâll put the car in the garage and then letâs talk.â

In a few moments the boys went into the house. Mrs. Hardy and Aunt Gertrude were relieved to see them, since it was long past dinnertime.

âYou must be starved,â Aunt Gertrude remarked. âAnd besides, the foodâs half ruined, standing here for over an hour!â

Mrs. Hardy smiled. âI donât think the boys will mind.â

The boys did not mind. They found the roast lamb, mashed potatoes, peas, and strawberry short-cake delicious. All the Hardys laughed over Joeâs description of Chetâs encounter with Lieber and the chocolate milk.

After dinner the brothers joined their father in his study. Frank was the first to tell his story, then Joe. Mr. Hardy listened with great interest.

âYou say the man who knocked you down wore a mask?â he asked Frank.

âYes! And if he was a ghost, he was a pretty solid one! By the way, Peterson has asked us to find the ghost! Shall we take his case?â

Mr. Hardy thought for several seconds before answering. âYes, take it. This so-called ghost seems to bob up a good deal. Heâs worth pursuing.â

The detective and his sons also agreed that the mysterious behavior of Zimm and Lieber could not be coincidence. It must be linked with the case, and the two were working together in some sinister plot.

Mr. Hardy warned his sons that they should be extra careful. âIf Zimm and Lieber are involved in the platinum thefts, and think you suspect them, they may make it sticky for you.â

âWeâll try not to flub again,â Frank promised.

âWhat do you plan to do next?â their father inquired.

âIâd like to drive out to Zimmâs house tomorrowâ morning,â Frank replied, âand investigate the area. We might be able to come up with a clue or two.â

âGood idea. Iâll keep on investigating at Stanwide itself.â

Early the next day Frank and Joe drove to Zimmâs house and cruised slowly past it. They saw that the garage, in which Zimm kept his car, was empty, and surmised that he had already left for work. The boys parked their car on the next block, then walked back toward the house. They tried to act nonchalant.

âThatâs where I ran into the masked stranger,â Frank said, pointing. âYou investigate that side of the house, and Iâll reconnoiter the grounds.â

Frank scanned the premises carefully, inch by inch. He saw the area of ruffled grass where he and the masked stranger had tumbled in their struggle. Unfortunately, even his trained eyes failed to detect a single clue.

As Frank continued the examination, his brother suddenly spotted something which startled him.

âFor Peteâs sake!â Joe exclaimed.

CHAPTER X

Startling Discoveries

FRANK rushed over to Joe. His brother was staring at something in a flower bed. Frank glanced down and was astonished at what he saw. There, deeply impressed in the soft dirt, were two footprints.

The instep of the right foot was narrower than that of the left. The prints appeared to be duplicates of those the boys had discovered in the concrete floor of the Stanwide hangar.

Clint Hillâs footprints!

âWhat do you make of it?â Joe asked his brother excitedly. âCould Clint Hill be alive?â

âThe reports certainly donât indicate it,â Frank replied. âBut if he is, why would he be sneaking around like this?â

âI wonder if the whole thing is a hoax,â Joe said. âMaybe Lance Peterson is using us to cover up a crooked deal he and Hill are involved in. They feel safe because they didnât count on our picking up the footprint clue in the hangar. Someone tried hard to keep us from seeing the prints. Maybe it was Hill himself!â

Puzzled, the boys decided to have another talk with Peterson. As they were about to leave, a window in the house was flung open, and a woman poked her head out.

âWhat are you doing here?â she shouted.

Startled, the boys looked up. âWe wanted to see Mr. Zimm. Is he at home?â Frank replied coolly.

âThen why didnât you come to the door, instead of prowling around out there?â demanded the woman in a rasping, unpleasant tone. âIâm Mrs. Zimm. What do you want with my husband?â

The Hardys realized that they could not reveal to Mrs. Zimm their reasons for being there. Perhaps she was in the plot with her husband! On the other hand, she might not know anything about his mysterious behavior, nor have heard any talk about Clint Hillâs ghost. In that case, the boys did not want to upset her.

âWeâre working on a job for Lance Peterson,â Joe ad-libbed, âand we wanted to ask Mr. Zimm some questions.â

âHe left for work about an hour ago,â his wife said indignantly.

âThen weâll see him there,â Frank told her.

She demanded that the boys leave at once. Glad to get away, they did not argue and returned to their car. Frank started for the Stanwide hangar.

âI could see by her face that Mrs. Zimm didnât know whether to believe us or not,â Frank commented.

Joe agreed. âI hope that when she tells Zimm we were here, it doesnât put him on guard.â

âIt wonât make much difference one way or the other,â Frank observed. âEither Zimm knows we suspect him of somethingâwhich means our prowling around wouldnât surprise himâor else he might really believe we came out to ask him some routine questions.â

When the boys arrived at the airport, they went at once to the Stanwide hangar. Lance Petersonâs office door was locked. As Frank and Joe strolled back across the hangar, they saw Jerry Madden come out of the operations room.

âIâve got a message for you!â he called to the Hardys. âMr. Allen has been trying to find you. He wants you to call him right away.â

Frank asked Jerry if he knew where Peterson had gone. Jerry said No, Peterson had taken the day off. Frank went to telephone Mr. Allen.

âWe are sending a large shipment of parts containing platinum to the Sun-Plat Tool Company in California tomorrow morning,â the executive told him. âOur company cargo plane will make the delivery. Lance Peterson and Aaron Lieber will be flying it. Because of the great value of this shipment, and the trouble weâve been having, as an extra precaution I would like you boys to follow in another plane. Can you do it?â

The Hardys excitedly agreed. âDonât worry about arranging for a pilot and planeâweâll handle that ourselves,â Frank said.

A short time later he and Joe were in the operations room of Ace Air Service, discussing the trip with Randy Watson.

âThe Stanwide cargo plane is a pretty fast ship,â Randy said. âWe donât have any equipment at Ace that would keep up with her. Iâll have to lease a special plane.â

âGo ahead and make the arrangements,â Frank told him. âBut keep it quiet.â

On the way home the Hardys stopped at police headquarters to ask them to check the license plate number of the car Joe had seen Lieber jump into. Detective Lieutenant Obels, a determined but pleasant man, sent the number to the motor vehicle department by police teletype. In a little less than an hour Lieutenant Obels called the boys at their home.

âHere it is!â the officer announced. âThe report says the car belongs to a Mr. Art Rodax.â

Frank thanked the detective, then hung up. âArt Rodax, our former boss!â he exclaimed, repeating the news to Joe.

âGood night! Heâs a pal of Lieber!â Joe cried out. âWell, weâre rounding up quite a group of suspects!â

Hoping to turn up another clue, the boys began calling all the camera stores listed in the telephone book. Not one of the shops reported having seen the stolen camera.

At five oâclock Mr. Freeman called Frank. The camera-shop owner said that the developed pictures had just arrived. âMr. Williams, the name under which the pictures were left, has already telephoned that heâs coming by for them.â

âWeâll be right over,â said Frank. âIf Williams shows up first, try to stall him.â

âOkay.â

When the boys drove up to the camera shop, they saw a large, burly man who seemed to be arguing with Mr. Freeman.

âThat isnât Zimm!â observed Joe. âMaybe he really does have a friend named Williams and he was delivering the rolls of film for him.â

âPossibly,â Frank agreed. âThen again, it might all be part of a clever plan to throw us off the track.â

The boys decided to demand a chance to inspect the films. As they entered the shop, Mr. Freeman turned to them with an air of relief.

âThis is Mr. R. C. Williams,â he said, indicating his customer. Then he turned back to the man. âThese boys believe that at least some of these pictures belong to them.â

âWhat!â shouted Williams. âThatâs crazy!â

âThen you wonât mind if we have a look at the prints,â Frank said politely.

âTouch my pictures,â Williams bellowed, âand Iâll sue every one of you!â

Mr. Freeman looked hesitant. He was thinking that perhaps the Hardys were being a bit hasty. At the thought of being involved in a lawsuit, he began to hedge.

âMaybe we have no right to ask Mr. Williams toââ he began.

âWeâll take the entire responsibility,â Frank interrupted. âMr. Williams can show us the pictures himself. We wonât touch them.â

Williams protested strongly. But seeing that the boys were determined not to let him out of the shop without seeing the pictures, he ripped open the big envelope, peered in, selected a few prints, and scattered them on the counter. None of the pictures belonged to the Hardys, they admitted.

âThere!â Williams sneered. âYou see? You guys ought to be thrown in jail!â

He quickly gathered up the prints and stuffed them back into the envelope.

âHow much do I owe you?â he snapped at Mr. Freeman.

âJust a minute!â Frank said coldly. âWe want to see all the pictures!â

âGet out of my way!â Williams shouted.

The shop owner, now more suspicious of Williams himself, offered to call the police. But at the word âpolice,â Williams paled.

âYou wonât have to do that!â he blurted. Reluctantly he reached into the package and displayed several more prints.

âI said we want to see all of them!â Frank demanded.

âThatâs all there are,â Williams insisted.

Joe reached out and seized the envelope. Shaking it vigorously, he spilled more prints onto the counter. The boys were elated to find that their suspicions were justified. Among the pictures were several aerial views they had taken!

Suddenly Williams let fly with his fists. He caught Mr. Freeman under the chin, and the shop owner slumped down behind the counter. Williams then whirled around and rushed the boys with his head down and arms flailing.

Frank and Joe, taken off guard, skidded on the highly polished floor and went down. Williams grabbed the pictures in his large fist and crammed them hastily into a pocket.

As the boys sprang to their feet, they saw Williams fleeing toward the rear exit of the shop!

CHAPTER XI

A Questionable Friend

FRANK and Joe darted after Williams and succeeded in intercepting him before he reached the rear exit. A wild struggle followed.

The boys and their burly opponent crashed to the floor in a mass of entangled arms and legs. Mr. Freeman, having recovered from the blow he had received, rushed over to give his support. Williams was exceptionally strong, but three against one was too much for him.

âThatâs enough!â he panted. âDonât hit me again!â He dropped and lay on the floor like a whipped dog.

âYouâd better do some explaining!â Frank said angrily as he and Joe stood up and brushed off their clothing.

Joe grabbed the envelope and extracted several pictures. âThe aerial shots!â he exclaimed, and handed them to his brother.

âIâve nothing to say.â growled Williams, trying to catch his breath. He sat up and ran a hand through his hair.

âWho stole our camera and films?â Frank demanded, glaring at their captive.

âI donât know about anything being stolen!â Williams insisted.

âOkay! Have it your way!â Frank declared. âMaybe youâd rather talk to the police!â The young sleuth walked to the telephone and began dialing a number.

Williams turned pale. âNo! Wait!â he pleaded. âIâll tell you all I know! Honest I will. Donât call them!â

Frank put down the phone. âGo ahead!â he ordered.

âMy name isnât Williams. Itâs Richard Tyson,â the man said, taking out his wallet. He displayed his driverâs license and a few credit cards.

The boys examined the cards and found the manâs address was the same as that of the apartment house in which Lieber lived.

âThen who is Williams?â Frank asked.

âWilliams rents a room across the hall from my apartment,â Tyson answered. âEarly this morning he asked me if I would pick up his pictures when they were ready. He told me to use his name.

âHe explained that the pictures were confidential and not to let anyone see them. Iâm sorry now I ever agreed to do it. I should have suspected something phony.â He got to his feet, brushed himself off, and looked at the boys nervously. âIâd like to leave,â he said, moving toward the door.

âNot until you tell us everything,â said Frank. âWho stole our camera?â

âI told you I donât know.â

âDoes Williams live alone?â

âNo, he rents the room from Mr. and Mrs. Lieber. The Liebers seem like nice people. I think Williams is Mrs. Lieberâs brother.â

The Hardys did not disclose that Mr. Lieber was already one of their strong suspects in the case.

âWell,â Frank announced, âyou can leave, but weâre going with you to your apartment. We want to check your story.â

âBy all means! Come along!â Tyson urged. He seemed eager for a chance to prove his innocence.

Frank asked Mr. Freeman to put the aerial pictures in his safe until the boys called for them. âWe donât want to risk their being stolen again.â

The brothers took Tyson with them, explaining that they would bring him back later to pick up his own car. As they drove, Tyson volunteered the information that Lieber was an airplane mechanic and stand-by copilot. As a result, he was away a lot. In fact, he often slept at the airport.

In a short time the group arrived at the apartment house. Tyson unlocked the main door with his own key. As they climbed the stairs, Frank said that he would like to find out whether Lieber was at home.

Tyson pointed to the door of the manâs apartment and Frank knocked. The door opened, revealing a stocky, handsome woman, with a tremendous amount of blond hair.

âHello, Mr. Tyson,â she said, seeing her neighbor.

âIs Mr. Lieber at home?â Frank inquired.

âNo,â she responded. âMy husband has to fly very early tomorrow, so he decided to stay overnight at the airport.â

âIs Mr. Williams at home?â Joe asked.

âHeâs not here, either,â the woman said. âIs it anything important? Can I take a message?â

âNo, thank you.â

Mrs. Lieber eased the door shut. Tyson led the Hardys to his apartment across the hall. There they met Mrs. Tyson, a short, middle-aged woman. She invited them to come in.

Frank casually conversed with her, selecting his words in such a way that the woman was not aware that he was probing for information. She told the young sleuth that Mrs. Lieber was a very secretive person who seemed extremely frightened of her husband.

âShe tries to forget her worries,â Mrs. Tyson said confidingly, âby always going to the movies and to parties. Poor thing. The Liebers never have any company.â

Momentarily satisfied with Tysonâs story, the Hardys drove the man back to the camera shop to pick up his car. He said little more to shed any new light on the mystery and was obviously relieved when the boys drove off.

When they reached home, Frank and Joe discussed the information they had gathered that day. âIâm convinced,â said Frank, âthat Lieber and this Williams are mixed up in the Stanwide case.â

âSo far, nearly all our suspects are company employees,â Joe commented. âHow does this fellow Williams figure in?â

âItâs possible that heâs part of the racket, but working from the outside,â Frank suggested.

The boys recalled Jerry Maddenâs remark about Lieberâs being Petersonâs pal. They wondered if this meant that the chief pilot himself was involved in the thefts.

âAnd it doesnât surprise me that Art Rodax fits into the picture,â said Joe. âI knew he had a secret reason for not wanting us around the plant.â

At that moment the telephone rang. The caller was Randy Watson. The pilot said that he had managed to rent an aircraft suitable for a long-distance flight from an operator at Lockwood Airport. This field was about two hundred miles from Bayport.

âIâve already been there and flown the plane back,â he said. âShe checks out fine. Weâll be ready to roll any time in the morning.â

âGood,â Frank answered. âJoe and I will be at the airport early. We canât risk missing Peterson and Lieberâs departure.â

At dinner the boys packed some light luggage. Mrs. Hardy and Aunt Gertrude tried to hide their anxiety when they heard the coming flight was to trail Peterson and Lieber, but an expression of concern crossed Mrs. Hardyâs face.

âDonât take any unnecessary chances,â she begged. âAnd keep in constant touch with us.â

Frank and Joe promised to do this. They assured the women that the trip was only routine, and that they would be away not more than two or three days.

âTwo or three days!â Aunt Gertrude exclaimed. âIf you catch those thieves the first day, why canât you come home? Thatâs where you belong, anyway!â

The boys grinned and Joe said, âWhy, Aunty, the longer the chase the more fun.â

âFun nothing!â she stormed. âA lot of dangerâunnecessary danger for a couple of growing boys!â Miss Hardyâs tirade ended only because she was called to the telephone.

Mr. Hardy, on the other hand, made no objection to the trip. âBest of luck, boys,â he said.

The following morning the boys started for the airport as soon as dawn broke. When they arrived, the Hardys spotted a sleek, highly polished twin-engine turbo-prop plane parked on the Ace Air Service ramp.

âThat must be the plane Randy rented!â Joe exclaimed, pointing. âMy, what a beauty! Wish I could fly her!â

Frank grinned in anticipation. âIt sure looks as if we wonât have any trouble keeping up with Peterson in that!â

The boys put down their bags and approached the plane for a closer look. Just then Randy Watson came running out of the operations building.

âHey, fellows!â he shouted excitedly. âCome here, quick!â

The young detectives ran to meet him.

âWhat is it?â Frank called. âSomething wrong?â

âI just tried to phone you at home,â Randy answered, âbut you had already left. Itâs about the Stanwide cargo plane!â

âWhat happened?â Joe asked.

âPeterson and Lieber left hours ago!â Randy said, trying to catch his breath. âThey took off late last night!â

CHAPTER XII

The Cave Clue

THE Hardy boys wasted no time. Moments later, they were dashing up the circular stairs to the Bayport control tower.

âIs Lou Diamond here?â Frank asked as they burst into the room.

âNo,â answered a lean, middle-aged man, who was seated at a desk. âThe chief doesnât come on duty for another hour yet.â

The brothers explained the situation to him and requested his help.

âI remember the Stanwide plane taking off,â the tower man recalled. âIt departed soon after I came on duty.â He quickly checked through his listing of aircraft movements. âHere it is,â he said, pointing out a small card. âThe plane took off shortly after midnight.â

âDid the pilot file a flight plan?â Frank questioned.

âYesâan instrument flight plan to a field in California,â the operator responded. âI canât tell you exactly, because normally we donât keep a record of flight plans here in the tower.â He picked up a telephone and snapped a toggle switch mounted on the desk. âIâll check with our communications station.â

It was several minutes before the operator received the information he requested. Then he placed the phone down and turned to the young sleuths. âThe Stanwide pilot canceled his flight plan at Chicago,â he said. âAfter taking on fuel, he departed without filing a new flight plan.â

Frank and Joe were dismayed. After thanking the tower man for his help, they left hurriedly.

âI want to call Mr. Allen right away and let him know what happened,â Frank said.

Mr. Allenâs voice was heavy with sleep as he answered the telephone. When he heard the news, however, he snapped awake.

âWhat!â he exclaimed. âPeterson didnât have authority to leave before the scheduled time. Meet me at the Stanwide hangar! Iâll be right over!â

The boys next called their father and informed him of the incident. Then they started walking toward the Stanwide hangar.

âPeterson and Lieber decided to vanish and keep everything for themselves,â Frank said. âThat was a valuable load they were carrying. It could make them rich.â

âPeterson might also be trying to escape Clint Hillâs ghost,â Joe added.

Mr. Allen arrived at the hangar and was aghast at the situation. He immediately placed a long-distance call to the Sun-Plat Tool Company in California, which was supposed to receive the air shipment. An official there told him the cargo plane had not arrived at the nearby airport. He assured Mr. Allen he would notify him the instant any information concerning the flight was received.

Turning from the telephone, Mr. Allen said to the Hardys, âI donât mind telling you Iâm pretty worried about this whole thing.â

The boys followed him to Petersonâs office, which they thoroughly searched. In the top desk drawer, Frank discovered a notation stating that Mr. Allen had ordered an earlier departure.

âI never gave such an order!â the executive declared. The young sleuths noted that the notation was typed, making it difficult to identify the writer.

They next went with Mr. Allen to interrogate the night watchman, who said Peterson had told him nothing. âI thought it was a funny time for him to be taking off, but itâs not up to me to question the actions of our companyâs chief pilot.â

âNo, of course not,â said Mr. Allen.

Using a master key, he searched Lieberâs locker but found no clues. Frank suggested they check the bills of lading for the Sun-Plat shipment. They scrutinized the records for more than an hour, but the results gave no hint of any tampering.

âWell,â Frank said, sighing, âthereâs nothing more we can do here.â

After assuring Mr. Allen they would continue tracking every possible lead locally, the Hardys returned to Randy.

âSorry our flight has been grounded,â Joe said wryly.

âToo bad. Well, Iâll just return the plane,â the pilot replied philosophically. âIâll be around if you fellows need me againâmaybe next time weâll have better luck.â

The boys, feeling somewhat let down, drove off. Frank suggested they go to the camera shop and examine the photographs Mr. Freeman was keeping for them.

âItâs a long shot,â he said, âbut maybe those pictures will tell us something.â

The boys arrived just as Mr. Freeman was opening his shop. He went to the wall safe, opened it, and handed them the negatives and prints. Joe picked up a magnifying glass from the counter. Mr. Freeman handed Frank another.

Meticulously the Hardys studied each of the aerial photographs. Several minutes passed before Joe suddenly cried out, âLook at this!â

Frank took the print and peered at it through his glass. Joe pointed to the rectangular pasture over which they had flown low before the engine of their aircraft had failed. âWhat do you see in the pasture area?â

Frank moved his magnifying glass slowly for a better focus. âI donât notice anything special,â he announced. âUnless you mean those three parallel lines running through the center of the pasture. They appear to be ruts, or grooves.â

âExactly!â Joe said. âWhat are they?â

âThe lines could have been made by a three-wheeled farm tractor,â Frank answered.

âOr maybe a small airplane!â Joe suggested.

âI wonder,â said Frank, then added, âRandy Watson told us the pasture was too short for any airplane to operate out of.â

âI know. Thatâs what has me baffled.â

Mr. Freeman, who had been watching the boys with interest, began glancing at some of the photographs. He asked in what locality the pictures had been taken. When the Hardys told him, his face broke into a wide smile.

âI thought I recognized the area,â he remarked. âWhen I was a boy, spelunking was one of my favorite pastimes. I used to go there a lot.â

âSpelunking?â Frank asked curiously. âYou mean you went exploring caves in that area?â

âOh, yes,â Mr. Freeman answered, obviously pleased at recollecting some of his childhood activities. âThere are several fine caves to be found in those hills. However, itâs been so many years since I was there, I wouldnât be able to locate any of them now.â

âHow large are the caves?â Frank asked, with increasing interest.

âThe ones I explored were rather small,â the shop owner explained. âI promised my parents I wouldnât tackle anything too deep. So I canât say just how large the bigger caves are.â

The boys thanked Mr. Freeman for his help, then started for home. Both were excited at learning of caves being in the area where they had seen Bush Barney. Perhaps, they speculated, the thieves were using a cave to hide their loot!

âThere might even be one near the pasture we flew over!â Joe exclaimed. âAnd if Iâm right about the deep grooves having been made by the wheels of a small plane, maybe itâs possible the pasture is being utilized as a makeshift runway after all!â

âI have an idea!â said Frank. âWhy donât we rent a helicopter and get a really close look at that area? But first letâs go home and tell the folks about our change of plans.â

Mrs. Hardy was elated to see her sons and to learn that their plane trip had been canceled.

Aunt Gertrude wore a self-satisfied grin. âGood thing,â she said. âNow you boys will have time for a lunch that will make up for the breakfast you raced through this morning.â

The Hardy family sat down to a meal of delicious homemade soup, followed by hamburgers, then gingerbread topped with applesauce and whipped cream. While they were eating, Frank and Joe related their conversation with Mr. Freeman, and told of their theory concerning a cavern hideout.

Mr. Hardy was interested at once. âA cave would be perfect for storing stolen merchandise,â he agreed. âIncidentally, Iâve learned that tract of land is part of an abandoned farm, but the whereabouts of the owner is not known.â

The boys discussed their plan to explore the area by helicopter. Their father approved, and suggested that they ask Randy Watson to make arrangements for hiring a craft and pilot.

Frank was about to make the call when the telephone rang. He picked it up. An eerie voice at the other end said, âIs this the Hardysâ house?â

âHi, Chet!â Frank said with a chuckle. His friend was imitating Clint Hillâs voice.

But as the unearthly voice continued, Frank realized it was not Chetâs! The words it spoke turned his blood cold.

âThis is not Chet,â intoned the speaker. âThis is the ghost of Clint Hill. Where is Lance PeterÂ· son?â

CHAPTER XIII

The Tornado

CHILLS ran up and down Frankâs spine and he stood motionless. He was about to answer that he did not know the whereabouts of Peterson, but then his momentary fright left him and he changed his mind. Frank decided to question the mysterious caller and perhaps get a lead as to his identity.

âIâll make a bargain with you,â the young sleuth proposed.

âWhat kind of bargain?â asked the voice, still in an eerie tone.

âIâll give you some information about Peterson,â said Frank, âif youâll tell me who you really are.â

There was a long pause.

âForget it!â said the sepulchral voice. âIâll find that double-crosser myself!â

âWait!â Frank urged. âDonât hang up!â

But a sharp clicking sound brought the conversation to an abrupt end. Disappointed, Frank shrugged, then dialed and made arrangements to rent a helicopter. In a few minutes he rejoined his family. They discussed the weird call from the âghost.â

Mrs. Hardy looked distressed, while Aunt Gertrude expressed contempt. âThese people who play tricks on the telephone!â

âYou say that this person called Lance Peterson a double-crosser?â Mr. Hardy asked.

âThatâs right, Dad,â Frank answered. âI wonder if our âghostâ actually is in cahoots with Peterson and Lieber, and was supposed to go with them aboard the plane, then found theyâd suddenly left without him.â

Father and sons continued to discuss this new development and its connection with the case, but failed to arrive at any conclusion. Presently Randy Watson telephoned and said he had made arrangements for Frank and Joe to fly in a helicopter the following morning. A minute later Mr. Allen called to tell the boys that authorities in the United States, Canada, and Mexico had been alerted to look for the missing company plane.

âAs yet nothing has been reported,â he said.

The next day Frank and Joe went to Bayport Airport. As they walked onto the parking ramp of Ace Air Service, Randy met the brothers and introduced them to Mack Carney, their pilot, young and well-built. A short distance away stood a small, three-place helicopter. Its cockpit was enclosed in a fishbowl-shaped Plexiglas canopy.

As the boys walked toward the craft, they glanced at the sky and noticed that a cloud cover was developing. Conditions to the south and southwest appeared especially bad. There, the bases of some clouds were darkening to an almost bluish black.

âLooks like a storm,â Joe commented. He feared that their flight might be delayed because of weather.

âThere shouldnât be any problem,â Mack reassured him. âIâve already checked the forecast. Ceilings and visibility are not expected to drop below visual flight rules at any time.â

He told the Hardys that scattered thunder-storms were predicted for the area, but that these could easily be avoided. By midafternoon the weather system was expected to move out to sea, with rapid clearing behind it.

Minutes later, the helicopter was aloft. The loud clapping of the whirling rotor blades, mixed with the noise of the engineâs muffler, bothered them for a few minutes. But gradually, as the craft gained height, turned and headed northwest, they ceased to think about it. The brothers settled back to enjoy the unobstructed view offered by the transparent canopy, and to watch the pilot.

âIâd like to learn to fly one of these,â Joe commented.

The flight took a bit longer than their previous trip to the area by airplane. As they flew into the sector they wanted to investigate, Frank scanned the ground below. He spotted the pasture in the aerial photograph and pointed it out to Mack. The pilot bent the helicopter into a series of turns around the field.

As he leveled the craft out on an easterly heading, Joe glanced to his right. Suddenly the boy detective sat rigid in his seat and stared from the window with an expression of disbelief.

âLook!â he shouted frantically.

The pilot spun the helicopter around to face in the direction Joe was pointing. Moving toward them was a black, funnel-shaped column of air, stemming from the base of an intensely dark cloud.

âIt looks like a tornado!â Frank yelled.

âIt is!â Mack exclaimed. âThey generally move in a northeasterly direction, about thirty to forty miles an hour. We might be able to outrun it.â

He whirled the craft around, but was greatly alarmed to find that their route of escape was blocked by the surrounding hills. The dark cloud base moving swiftly overhead cut off the possibil ity of climbing out over the top of the higher terrain.

âThe tornadoâs getting closer!â Joe shouted

âWhatâll we do? That tornado is getting closer!â Joe shouted.

âWeâll have to head for the ground!â the pilot replied grimly.

As the menacing funnel approached, the surrounding air became turbulent. Mack struggled with the controls as the craft was thrown about viciously. Frank and Joe braced themselves as best they could, while the pilot tried to establish a controlled descent.

Suddenly Frank and Joe looked out to see a strange phenomenon. The funnel-shaped column seemed to divide in half, as if sliced by an invisible knife. The upper half veered off in a northeasterly direction, while the lower half maintained its original path, passing close to the bobbing helicopter.

âIâm losing control!â Mack shouted. âHang on! We must be close to the ground!â

The violent jolt of landing almost knocked the helicopterâs occupants unconscious. They sat dazed for several minutes before regaining their senses.

Then, gradually, the three became aware of a complete calm. The tornado and dark cloud had disappeared, and not even a breeze was stirring. The sky showed signs of clearing.

âWow!â said Joe. âI hope that never happens to me again!â

âWeâre lucky to have got out of this in one piece,â Mack said grimly

He got out of the helicopter, followed by the Hardys, and began to examine the craft for damage. The boys, glancing around, realized that they had landed on a corner of the pasture.

âHowâs the copter?â Frank asked.

âThe landing gear is sprung, and thereâs some structural damage here and there,â Mack observed. âIt doesnât appear to be serious, but Iâd better give the craft a thorough inspection before we attempt to fly it out of here.â

Frank and Joe decided to investigate the area while the pilot conducted his inspection. They started walking down the pasture toward the high hill situated at the far end.

âHere are those grooves we saw in our photos,â Frank remarked. âThey go from one end of the field to the other.â

He took a tape measure from his pocket and carefully noted the width of the grooves and the distance between them. Pulling out a pencil, he jotted down the figures in his notebook for future reference.

âI still think these grooves were made by the wheels of an airplane,â said Joe.

âBut how? The length of the pasture rules out the possibility that a plane could land here,â Frank objected.

The boys continued heading for the hill at the far end. Just short of the tree line they stopped and peered into the murky shadows of the woods. The hill began to slope sharply upward at this point.

âI donât see any caves around here,â Joe observed.

The boys were about to proceed closer when suddenly a man darted out from the woods. The boys recognized him immediately as the stranger who had previously challenged them near this spot. He was now unarmed.

âWhat are you doing here?â he bellowed. âGet off of this land! Itâs private property!â

âWe were forced down by a storm,â said Joe, pointing toward the helicopter just visible in the distance.

âThe storm is over!â the man retorted. âNow youâd better climb into that bird and get out of here!â

âBut we donât know if we can take off,â said Frank. âWe got bounced around pretty bad in the storm. The copter was damagedâhow much, we donât know. Our pilot is inspecting it now.â

âIf it wonât fly, youâll just have to leave it!â the man growled, his face purpling with anger. âI want you to get out of hereâand fast!â

Meanwhile, out of the corner of his eye, Joe glimpsed a flicker of movement in the woods. He turned his head cautiously in an effort to get a better view. What he saw caused him to grab his brotherâs arm as a signal not to argue further.

Concealed behind a tree was someone with a vicious-looking hunting bow. An arrow had already been fitted to the string, and was now aimed directly at the boys!

CHAPTER XIV

Amazing Camouflage

WITHOUT further protest, the Hardys turned and started walking back toward the helicopter.

âTake a quick look to your left, Frank,â whispered Joe. âSomeoneâs aiming an arrow at us!â

After taking a few more steps, Frank glanced over his shoulder. At that instant the man armed with the bow and arrow darted from behind one tree to another. The boy detectiveâs keen eye recognized his face immediately.

âBush Barney!â Frank said softly.

The brothers reached the helicopter just as the pilot was completing his inspection.

âThereâs some minor damage,â Mack reported, âbut not bad enough to prevent us from flying if we have to. You in a hurry?â

âYes,â said Frank, âwe must notify the police about two men who chased us!â

âI canât radio from here,â Mack told him. âBut as soon as weâre airborne, there wonât be any interference.â

âAfterward,â said Frank, âwe can come down again and land somewhere out of sight of the pasture and walk back here to meet the officers.â

âSuits me,â said Mack. âI donât like the sound of this motor yet and Iâd just as soon come down and work on it some more.â

In a few minutes the whirling rotor blades were carrying the young detectives skyward. Frank asked Mack to radio Bayport tower.

âOur transmitter doesnât have enough wattage to reach that far,â the pilot said. He extracted a sectional air chart from his kit and examined it. âThereâs an omni radio station with voice facilities much closer to us,â he announced. âIf we climb above these hills, we should be able to establish contact, and have them relay a message for you.â

Mack tuned the radio dials to a standard aviation communication frequency, then picked up the microphone and gave his identification number and approximate position. In seconds the speaker on his receiver crackled a response. Mack handed the microphone to Frank and told him to proceed with his message.

Frank requested that word be relayed to the State Police to meet the Hardys at the pasture. He estimated the pastureâs location along the secondary road, and as a double check gave its longitude and latitude coordinates from the air chart. Several minutes passed before a response came through.

âThe State Police,â the station operator reported, âhave been notified. Several officers are on their way to the location you indicated.â

Frank asked Mack to land them close to the pasture, but to approach the area from behind a hill so their craft would not be seen. Mack nodded and began a rapid descent between the hills. He followed a valley that led them back in the general direction of the spot where they had been forced down. Approaching from behind a hill close to the pasture, he maneuvered the helicopter to a soft landing in order not to strain the already partially damaged landing gear.

âMack, youâd better wait for us here and guard the copter,â Frank suggested.

âWill do.â

The boys carefully picked their way among the trees and brush toward the pasture. Soon it came in sight. Frank and Joe did not speak. They communicated by sign language, which they had practiced until they could use it to perfection.

As silently as a couple of Indians, the Hardys edged their way to the hill situated at the end of the pasture. They stopped for a moment and scanned the dim shadows of the woods. Both of them listened for unusual sounds, but neither saw nor heard anything out of the ordinary.

Frank signaled his brother, indicating that they should proceed on up the slope of the hill. Suddenly he tugged at Joeâs arm and pointed directly ahead.

Joe stared before him, but could see only an unbroken mass of trees and bushes. As he stepped closer, however, the trees in the foreground gradually took on an unnatural aspect. It was difficult to tell exactly why, but there was something odd in the way the trunks and leaves reflected the light.

Approaching still closer, the Hardys were amazed to see what really confronted them. Spread across a portion of the steep slope was a huge piece of heavy canvas! Painted on its surface were trees, grass, boulders, and bits of brush. The representation was so well done that it was not detectable unless viewed from within a few feet of the canvas.

âItâs fantastic camouflage!â Joe remarked, breaking their silence for the first time.

âSure is,â Frank agreed, gazing at the canvas almost in disbelief. âIâm willing to bet that behind this is the opening to a cave!â

The young sleuths traced the canvas to where it terminated at one side. Together, they carefully pulled it aside far enough to get a glimpse of what lay behind.

A huge opening was revealed. The Hardys peered inside. Although the interior was practically in blackness, they could see that it was the entrance to a very deep cave of immense size!

Each boy took a pocket flashlight and directed the beams into the darkness. So deep was the cave, however, that the lights appeared to fade off into nothingness.

âI donât hear a sound,â Frank said. âIt must be empty.â

âLetâs take a look around!â Joe suggested, his voice tense with excitement.

âOkay!â Frank agreed. âBut weâll have to let the police know where we are. Iâll stay here and keep an eye on the cave. You go back to the copter, tell Mack about this place, and ask him to send the police here.â

Joe started off at a sprint. Frank positioned himself behind some real brush near the camouflaged entrance. It was not long before Joe came bounding back.

âEverythingâs all set,â he said.

The boys pushed their way around the edge of the canvas and stepped into the cave. As their eyes became accustomed to the dark interior, they could make out rough rocky surfaces curving into an arch high above their heads. The faint sound of their footsteps was amplified in a series of echoes that seemed to bounce back at them from all sides. Frank played his beam of light toward the floor.

âLook!â he said. âThere are wheel grooves in here, just like the ones we spotted on the pasture.â

The Hardys followed the ruts deeper into the cave. After advancing for several yards, Joe suddenly came to a stop.

âAn airplane!â he exclaimed, astounded.

Frank pointed his flashlight in the same direction. The beams picked from the darkness a sleek, multiengine plane with tricycle landing gear.

âIt was taxied in here!â Joe marveled.

âFrom the pasture,â said Frank. âThe floor of this cave is about on the same level as the field, and is right in line with it. The pasture itself is too short to land on or take off from. But this cave floor serves as an extension of the runway. When a plane lands, someone on the ground merely pulls the canvas camouflage aside andâprestoâa plane has several hundred feet more to roll on!â

Joe nodded. âAnd when it comes to rest, inside the cave, itâs automatically hidden. Very clever. Could this plane be the same one that toppled our car?â

âI canât say for sure,â his brother responded, âbut thereâs a good chance it is.â

The Hardys continued exploring the cave. A little farther on they spotted a large wooden door. It was padlocked, but they noted that the hinges were not very strong. Each boy pushed hard against a section of the wood. It began to crack, then finally gave way with a resounding smash.

Frank and Joe stepped into a room formed out of the natural rock. They were astonished to see stacks of sturdy wooden boxes piled along the walls. Stamped on the side of each was: STANWIDE MINING AND EQUIPMENT COMPANY.

âWow!â Joe exclaimed. âThere must be fifty or more of these boxes here!â

âAnd they may contain the stolen platinum parts!â Frank said as he played his light across the stacks. âLetâs break open one of the boxes and check.â

The boys placed their flashlights on the floor and positioned the beams toward one stack of boxes. They then walked over, dragged off the box on top, and set it on the floor.

âWhew!â Joe was puffing. âIt sure is heavy.â

âWeâll need something to pry open the lid,â Frank said, glancing around.

Joe noticed a rusted metal rod lying on one of the stacks. He took it and forced the end under the lid of the box. Then both boys put all their weight against it. After much exertion, they began to loosen the top.

âItâs beginning to give a little,â Joe said.

They had nearly accomplished their task when the sound of footsteps interrupted them. The Hardys froze.

âHands up!â growled a gruff voice from behind them.

CHAPTER XV

Capture

THE surprised boys whirled to find themselves face to face with Bush Barney and the man they had recently encountered in the pasture.

âWhat are you guys doing here?â the latter snarled. âI told you to get out!â The man fingered the muzzle of his shotgun, which now was pointed at the ground.

Frank and Joe were at a loss for an excuse as to their presence in the cave. Frank realized that nothing he could say would sound believable. But anything was worth a try at this point, he thought.

âWe took off in the copter,â he explained nonchalantly, âbut it wasnât working right so we landed again. While our pilot was checking the engine, my brother and I decided to walk around a bit. It was quite by accident that we stumbled on this cave.â

Bush Barney turned on a bright electric lantern and hung it on a metal spike hammered into the stone wall of the storeroom. His expression was grim.

âI donât believe a word of it!â he snapped, glancing at his companion. âIâll bet these punks already knew about the cave. They might have even been in here before.â

His confederate gripped the shotgun more tightly. To the boysâ relief, he did not raise it.

âIs that right, boys?â he bellowed. âWere you ever in here before?â

âNo!â Joe cried out. âAs my brother told you, we discovered the cave just nowâby accident!â But the Hardys could see that the two men were not convinced.

Frank tried to estimate the time that had passed since the police were notified. They should be arriving soon, he told himself. In the meantime, he and Joe must keep these men talking.

âAnchor!â said Barney, addressing his partner. âYou keep âem covered while I find some rope.â He went out.

The young detectives stood helpless, churning with anger at their predicament. There was no chance for them to attempt to rush at Anchorâhe was watching too closely.

Minutes later, the ex-convict Bush Barney returned to the room, carrying a large coil of rope. He took the shotgun, then handed the rope to Anchor.

âIâll hold this while you tie âem up,â he said.

Barney motioned the boys to put their hands behind their backs, and Anchor uncoiled the rope. Suddenly the sound of approaching footsteps caused the two men to stiffen.

âAnyone in here?â shouted an authoritative voice. âWeâre the police!â

âQuick! Dowse that light!â Anchor growled to Barney, pointing to the electric lamp hanging from the spike. He then reached out to retrieve his shotgun from Barney.

The Hardys glanced at each other. This was their chance to act! Joe spun around, kicking the shotgun out of Anchorâs hands just as it was handed over.

Frank rushed Barney. Before the ex-convict could turn out the lamp, the young sleuth sent him crashing to the floor with a perfect tackle.

Joe managed to catch Anchor in a tight head lock and tumbled across the floor with him. Barney reached for the shotgun, but Frank grasped it first and threw it a distance away. With his free arm he then swung at Barney, catching the ex-convict directly on the chin. His opponent fell back, stunned.

At that instant four state troopers rushed into the room and helped the boys drag the two men to their feet. The suspects were immediately handcuffed.

âNow how about answering a few questions?â Frank demanded.

The captured men glared at the boys malevolently.

âWe donât know anything!â Barney growled.

âWho owns the airplane thatâs kept here in the cave?â Frank pressed.

âYou wonât get anything out of us!â boasted Anchor.

âDo the boxes in this room contain merchandise stolen from Stanwide?â Frank continued.

The men remained stubbornly silent. The Hardys guessed it would be a waste of time to keep on trying to elicit any information from them. So they decided to get in touch with Mr. Allen and ask him to come to the cave. The boxes would be opened in his presence with the police officers as witnesses. This might help to build an airtight case against the racketeers.

âWe can reach headquarters on our car radio,â said one of the troopers when Frank explained the boysâ plan. âWant to come along and send the message yourself?â

âThanks.â

Leaving the others to guard the two prisoners, Frank and an officer walked to the police car, parked on the road. The trooper established contact with his headquarters and Frank described the situation to the chief. Shortly a response was received telling them that Mr. Allen had been reached and would leave at once for the cave. In order to save time, a police helicopter would bring the executive to the site.

Meanwhile, Frank and the officer returned to the cave. Barney and Anchor appeared increasingly nervous. The boys hoped they would break down and answer the Hardysâ questions. They still refused to speak, however.

After what seemed like an eternity of restless waiting, the sound of a helicopterâs whirling rotor blades was heard faintly in the distance. The Hardys darted from the cave and into the center of the pasture. They waved their arms vigorously as the craft passed overhead. In response, it turned into a descending spiral and the pilot set the craft down gently a few yards away from the boys. The door opened and Mr. Allen stepped out.

âYou two have discovered something of great importance?â he asked eagerly.

âYes, we have,â Frank answered. âWeâve captured two members of the gang we think is involved in the platinum thefts, and what may be the stolen merchandise.â

âCongratulations!â Mr. Allen said. âYou donât waste any time when working on a case.â

âThanks,â Frank replied. âBut the mystery is far from being solved. Thereâs a great deal more that weâll have to uncover.â

The sleuths took the executive to the cave. âIncredible!â he commented, awe-stricken. âHow did you ever manage to discover this hideout?â

âWeâll fill you in on the details later,â Frank said. âRight now, weâd like you to check out the contents of the wooden boxes we found here.â

As they came to the plane, he stared in astonishment, but did not pause. The three hurried on to the waiting group, and the executive was introduced.

As Mr. Allen and the two boys entered the storage room, Barney and Anchor looked very uneasy. The president of Stanwide took several folded sheets of paper from his coat pocket.

âThese are copies of the bills of lading of the missing shipments,â he said. âIâve checked off what materials made up the shortages.â

The Hardys lifted the lid of the box they had been opening, and Mr. Allen read off a list of items and quantities. The contents tallied exactly with some of the missing platinum parts! Two other boxes were opened, disclosing more of the items on the list!

Frank spoke to the officers. âIâd say thereâs enough evidence here to arrest Barney and Anchor.â

âYouâre right,â said one of the State Police officers.

Gripping each of the handcuffed men by an arm, two of the troopers began walking them out of the cave.

Suddenly Anchor broke his silence. âWait a minute!â he shouted. âYou canât do this! Weâre not the head guys in this racket!â

âWho else is in this with you?â Frank prodded. âGive us their names!â

Barney nudged Anchor with his elbow, signaling him to keep silent. âI donât know who they are,â Anchor mumbled meekly.

Refusing to say any more, the two suspects were led away. Mr. Allen clapped the Hardys on their shoulders. âThis has been a great job on your part, fellows.â The brothers grinned.

With their help Mr. Allen checked several more boxes and found that they also contained stolen parts. Joe suggested that they load as many of them as they could aboard Mackâs helicopter for transport back to Stanwide. One of the troopers offered the use of the police helicopter to aid in the operation. He also told the Hardys that several men would be assigned to stand guard over the cave.

Still amazed by the camouflaged hideout, Mr. Allen took a flashlight and scanned the surroundings. For the first time he took a close look at the airplane stored there. What he saw seemed to startle him.

âItâs hard to believe!â the executive murmured. âBut it is!â

âWhat is?â asked Frank, curious.

ââThis airplane!â Mr. Allen answered, playing the beam of light across its sleek lines. âThis was Clint Hillâs!â

âBut I thought that crashed!â Joe said in amazement.

Mr. Allen beckoned the Hardys to step closer to the plane. He pointed a trembling finger at something on the side of the cowling. It appeared to be a small decal, in the shape of an eagle.

âClint put this emblem here,â the executive said. âThis was his personal airplane.â

The boys did not speak, noting that Mr. Allenâs face expressed deep sadness. Slowly walking around the plane, he stopped at the cockpit door, opened it, then climbed inside. He sat there quietly, as if expecting the lost pilot suddenly to appear.

CHAPTER XVI

Telltale Initials

GLANCING at each other, the Hardys kept silent as Mr. Allen continued to stare sorrowfully into space. They were eager to ask him more about Clint Hillâs plane, but out of respect did not disturb him. He sat quietly in the cockpit for several minutes, then finally climbed out.

âI assume the airplane was sold after Hillâs accident,â Frank said. âWho bought it?â

âIt wasnât sold to anyone,â Mr. Allen replied. âThe plane was stolen soon after Clint crashed.â

âStolen!â the boys cried out.

âYes,â Mr. Allen answered. âI had almost forgotten the incident.â

He went on to explain that local and government authorities had investigated the theft, but had turned up nothing.

âWe finally came to the conclusion,â Mr. Allen said, âthat whoever stole the plane either crashed in it, or shipped it out of the country.â

âMaybe Hillâs ghost stole it,â Joe muttered derisively.

Then another angle occurred to the boys. If Clint Hill had survived the crash at sea and was involved in the platinum racket, had he come back to steal his own airplane for use in the thefts?

Returning to the business at hand, Frank and Joe, aided by Mr. Allen and two troopers, dragged some of the boxes from the cave and the task of loading the stolen material aboard the police helicopter was begun. When the craft was packed to capacity, its pilot quickly departed for the trip back to Stanwide.

Meanwhile, Joe had hurried off to get Mack and his helicopter. Soon the craft arrived, landing on the pasture near the cave entrance. The pilot jumped out and went into the thievesâ hideout to pick up more boxes for loading. As they emerged from the cave, an eerie, disembodied sound brought them to a stop. Someone unseen was whistling âHigh Journey.â Mr. Allenâs face turned ash white.

The whistling stopped. It was followed by a ghostly sounding voice. âYou canât escape from a man youâve killed!â

âThatâs Clint Hillâs voice!â Mr. Allen gasped. He was trembling.

âWhere is it coming from?â Joe asked.

âListen!â Frank ordered as the whistling began again. He made an effort to determine its source. Suddenly Frank, followed by his brother, broke into a fast run toward the helicopter. They reached the craft just as the whistling ceased.

âItâs coming from the radio receiver!â Frank shouted in amazement.

âWhatâs going on around here?â asked Mack, completely baffled.

âI wish we knew,â Frank responded, staring at the receiver.

Mr. Allen now joined the boys and Mack. âIf I wasnât so sure that it was Clint Hillâs voice we heard, Iâd say the whole thing is a hoax,â said Mr. Allen with a grimace.

âI donât believe itâs just a hoax,â Frank assured him. âAnd now shouldnât we start loading the boxes aboard?â he suggested, hoping to take Mr. Allenâs mind off Hillâs ghostly message.

The work was arduous, but soon the helicopter was filled to capacity, reserving enough space so that Mr. Allen could return to Stanwide with his property. The Hardys asked Mack to pick them up later.

âWhile weâre waiting, weâll do more sleuthing in this area.â

When all the cargo was secured, Mr. Allen shook hands with the boys, thanked them again, and boarded the helicopter. The pilot started the engine and set the rotor blades at a high RPM for take-off power. The craft lifted off the ground, then headed on a course to the southeast. It quickly disappeared beyond the crest of hills.

Frank and Joe returned to the cave. Two troopers had posted themselves at the entrance. The brothers went inside to take a closer look, beaming their flashlights at every inch of the rocky interior. They found nothing of significance.

Finally Joe went to the very rear of the cavern to search.

Frank, meanwhile, walked over to the airplane and climbed into the cockpit. Looking toward the rear, he spotted a small but powerful electric hoist mounted on rails that straddled a hatch in the floor of the cabin. Several hundred feet of light cable were wound around the hoistâs spindle.

âWhatâs a device like this doing in a passenger airplane?â the young detective puzzled. âAnd whatâs it used for?â

Making a mental note of the hoist, Frank turned his attention to other areas of the cabin and cockpit. He searched through all the compartments but all he found were some air charts and an old navigational plotter.

âWhoever stole this plane made sure he left nothing around to identify him!â Frank muttered.

He extracted a fingerprint kit from his pocket and dusted the wheel, instrument panel, throttle, and other normally exposed areas for telltale prints. As he had expected, there were none; the occupants had been clever enough always to wear gloves.

Frank now bent low with his flashlight and searched underneath the seats. Suddenly he noticed a small leather object jammed between those of the pilot and copilot. He had difficulty reaching it, but finally managed to grasp the object and pull it out. A leather glove!

The young detective examined the lining of the fairly new glove. What he saw caused him to shout in excitement. Marked on the lining with indelible ink were the initials L.P.

âLance Peterson!â Frank exclaimed, bolting out of the plane.

Excitedly he called to Joe, who came running. âWhatâs up?â

âLook!â Frank cried, thrusting the glove toward his brother.

Joeâs eyes widened as he spotted the initials. âThey must stand for Lance Peterson!â

âRight! Mr. Allen should know about this as soon as possible!â

The boys hurried from the cave and told the troopers of their discovery. One of the policemen took his walkie-talkie radio out of its case, pulled the telescopic antenna from its housing, and flipped a toggle switch.

âThese units canât transmit more than a mile or two,â the trooper said. âBut one of our patrol cars might be within range somewhere. They can get a call through to Mr. Allen.â

The trooper succeeded in reaching a patrol car and transmitted the message. While awaiting a response, the boys discussed Petersonâs connection with the racket.

âHe must have stolen Clintâs plane himself,â Joe surmised.

âIt sure looks that way,â said Frank. âBut if Peterson is using the plane to fly in the stolen loot, I wonder where he makes the pickup. It certainly couldnât be Bayport. The airplane would be recognized there at once.â

A crackling sound from the trooperâs walkie-talkie signaled them that a message was about to come in. The policeman put the receiver to his ear and listened intently. After a couple of minutes he put down the instrument and turned to the boys.

âMr. Allen has just arrived back at Stanwide. He has received your message and congratulates you on the new clue. Also, he wants you to know that he checked with Bayport tower and was told that nothing new has turned up on the whereabouts of Peterson and Lieber.â

âThanks,â said Joe.

He suggested to his brother that since it would be another couple of hours before the helicopter returned to pick them up, they do some investigating outside the cave.

âGood idea, Joe. Say, do you remember the small cabin I spotted when we flew around here with Randy Watson?â

Joe nodded.

âIâd like to take a look at that place for clues,â Frank told him. He pointed off across the road, in the direction of the heavy woods there. âIf I remember correctly, the cabin should be located about a mile from here.â

The Hardys told the troopers where they were going, and said they should be back in about an hour. They started off at a fast pace.

âThis sure is tough traveling,â Joe remarked as they picked their way up a hillside among closely spaced trees and tangled brush.

âItâs rugged,â Frank agreed. âBut we ought to be getting close to the cabin soon.â

The boys continued to plod ahead. Finally Joe tugged at Frankâs arm and pointed to a small clearing a little to his right.

âThe cabin!â he whispered.

The boys proceeded cautiously and stopped at the edge of the clearing. The cabin was weather-beaten and dilapidated.

Again Joe pointed. âLook! The doorâs halfway open!â

âThere doesnât seem to be anyone around,â Frank answered in low tones.

The boys bent down and edged their way closer. They stepped with meticulous care to avoid making any noise. Suddenly the cabin door slammed shut with a loud bang. Startled, the boys quickly dashed for cover behind a large tree and focused their eyes on the building.

CHAPTER XVII

A Revealing List

TENSE and excited, Frank and Joe watched the cabin door. Suddenly it swung open, then slammed shut again. During the next few moments this cycle was repeated several times.

âWhatâs going on?â Joe whispered.

Frank glanced at the surrounding trees. He noticed that the leaves were moving, and grinned.

âItâs the wind,â he said. âThe door is being blown open and shut. It must have a faulty latch.â

The boys studied the cabin for a sign somebody was around. When they were fairly certain that no one was nearby, they stepped from behind the cover of the tree.

âIâm going into the cabin,â Frank announced. âYou stay on guard here.â

âBe careful,â Joe urged. âIf you need help, just yell.â

Frank slowly approached the cabin. The door swung open and was about to slam shut again when the young sleuth grabbed the knob. Stealthily he poked his head inside the building.

The cabinâs one small room was in deplorable condition. Unwashed dishes were piled in a metal basin, articles of clothing were scattered about, and dust lay everywhere. âWouldnât Aunt Gertrude fuss if she could see this mess!â Frank said to himself, chuckling.

He stepped into the room and looked around for clues. At one end was a stone fireplace in which were scattered several charred logs. Flanking each side of the fireplace were numerous boat anchors of varying shapes and sizes. âThis is Anchorâs place, all right,â thought Frank. âI can see how he got his nickname.â

The young detective spotted a supply of canned foods, stacked on a wooden shelf above the sink. Realizing he was hungry, Frank opened a couple of cans of meat. He then took them outside and shared their contents with Joe.

âAnchor brand meat, eh?â Joe grinned. âRemind me to thank that crook!â

Frank returned to the cabin to continue his investigation. After a thorough search, he found nothing. Frank was about to give up when something in the fireplace caught his eye. It was a charred piece of paper. Lifting it carefully out of the ashes, he placed it gently on the floor.

Bending down, the young sleuth saw that it contained a list of names. The printing was extremely faint, but he could make out the names Peterson, Anchor, and Rodax. At the bottom of the list was a skull and crossbones and the initials C.H.

âC.H.,â Frank repeated. âCould they stand for Clint Hill?â

On a hunch Frank picked up a bucket of fire-wood located nearby and dumped the contents on the floor. Among the wood was a crumpled fragment of paper which appeared to have been torn from a small loose-leaf diary. Frank smoothed out the paper and found written on it:

That ghost knows too much!

Excited, Frank rushed outside to show Joe his discovery. Joe examined the note, then pointed to a patch of ground near the cabin.

âIâve made an interesting discovery of my own,â he said, and led Frank to the spot. Impressed clearly in the earth was a set of footprints. The instep of the right foot was narrower than that of the left.

âClint Hillâs footprints again!â Frank exclaimed.

âAnd they appear to be quite fresh,â Joe said.

Frank stared at the prints. âNow Iâm convinced Clint Hill is alive! If he was double-crossed by the gang, maybe heâs plaguing them for revenge, or to extort money from them in return for keeping quiet about their activities.â

âThat could be the reason why Peterson wanted us to track down the ghost,â Joe replied. âOnce we found Hill, he could get rid of him.â

âPossibly,â Frank said. âThen again, we could have Hill all wrong. He could be working to bring the gang to justice in his own way.â

Frank took an envelope from his pocket and gently inserted the charred piece of paper he had found.

âMack should be here soon to pick us up,â he said. âWeâd better get back to Bayport pronto and show this new evidence to Mr. Allen.â

The boys returned to the pasture. They had waited only a few minutes when they saw the helicopter skimming over the tops of the hills. The pilot descended directly over the pasture and touched down a few yards away. The boys climbed into the cabin and the craft lifted off the ground.

A brisk tail wind carried the helicopter along at a ground speed greater than that normally experienced, shortening the return flight by almost fifteen minutes. Mack set the craft down on a grass-covered area near the Ace Air Service ramp, and the Hardys hurried off to telephone Mr. Allen.

âIâll meet you at Petersonâs office in a few minutes,â he said.

Minutes later, the two detectives were walking through the company hangar. They noticed that all of Stanwideâs aircraft were out except one. As the Hardys passed it, a man suddenly jumped from behind the plane and, unnoticed by the boys, lobbed a spherical-shaped metal object at them. It struck the concrete floor, bounded hard once, then rolled directly toward the brothers.

âHit the floor! Quick!â Frank shouted as he recognized the object. âThatâs a hand grenade!â

The boys hurled themselves flat and folded their arms over their heads. A split second later they heard an ear-shattering explosion, then the piercing whine of shrapnel flying above them.

The concussion rocked the hangar. Metal fragments from the grenade tore into the wings and fuselage of the plane. The high-octane fuel gushed out of the planeâs wing tanks, buckled by the blast.

Half dazed, the boys scrambled to their feet. The churning dust and smoke choked them.

âWeâd better get out of here!â Joe cried out. âIf that fuel catches fire, this place will go up like a torch!â

Outside the hangar, the Hardys glanced around to see if the man who had thrown the grenade was in sight, but he had vanished. A small crowd had gathered, attracted by the explosion.

An airport fire truck rolled into the hangar. Its crew quickly sprayed the plane and the floor with chemical foam to prevent the fuel from igniting.

Just then Mr. Allen arrived. âWhat happened here? Whatâs all the commotion?â he asked.

âSomeone tossed a grenade at us in there!â Joe answered, wiping beads of perspiration from his forehead.

âThe gang weâre after sure plays rough!â said Frank, angered.

Mr. Allenâs face showed his apprehension. âThings are becoming too dangerous. Maybe you boys should give up the case.â

âWeâre not quitting now!â Frank declared. âWe have the gang worried. Theyâre desperate, and want us out of the way. This grenade business proves it.â

The Hardys and Mr. Allen walked together to Petersonâs office. There, Frank showed the executive the names on the paper he had discovered in the cabin.

âThis ties in with some news I have for you,â Mr. Allen said. âI have just learned that Rodax has suddenly resigned his job. He told the payroll master, who was the last to see him, that he had been offered a better job with another firm.â

âDid Rodax say where?â Frank queried.

âNo, only that it was a long distance from here. He collected what pay was due him and disappeared.â

âHow about Mrs. Rodax?â Joe asked. âHas anyone questioned her yet?â

âI telephoned his home,â Mr. Allen said. âMrs. Rodax informed me that her husband left and did not say what his destination was. He told her only that he was going on a confidential trip.â

âWhat time did Rodax leave the plant?â Frank asked.

âLate this morning, according to the payroll master.â

âThen itâs too late to try tailing him,â Frank said, disappointed.

âAnother thing,â the executive said. âOne of the shipping-room clerks, John Unger, also quit his job suddenly.â

Frank remarked, âHe too could be working with the gang.â

Joe stood nearby in deep thought. âI have a hunch,â he said. âItâs pretty obvious they never did reach California, and no word has been received of their landing anywhere else in this countryâor Canada or Mexico.â

âWhere do you think they are?â Mr. Allen asked with interest.

âIle de la Mer,â Joe answered. âSince itâs uninhabited, it would make a great hideoutâand Peterson would remember the air route from the trip he and Clint Hill were making when their plane crashed at sea.â

Both Frank and the company president were impressed by Joeâs theory.

âItâs worth looking into!â Frank exclaimed, and turned to Mr. Allen. âCould you arrange for Joe and me to go there?â

âI certainly can,â Mr. Allen said. âBut not without protection. Iâm going to assign a husky body guard to accompany you!â

CHAPTER XVIII

Air-Chart Secret

ELATED at the prospect of the trip, the brothers hurried home to discuss the island hop with Mr. Hardy. The ace detective was apprehensive, especially after hearing about the grenade incident. He agreed, however, that a search of lie de la Mer would certainly be worthwhile.

âIâd like to make the trip with you,â their father said. âBut there are too many loose ends in the case to be taken care of here.â His expression became grave. âBe on your guard,â he warned his sons. âThis is a clever gang weâre up against.â

The Hardys were just finishing dinner when Mr. Allen telephoned. âIâve obtained the use of a twin-engine amphibian aircraft to take you boys to Ile de la Mer. Jerry Madden will be your pilot,â the executive announced. âIâve also managed to get two big, strapping fellows from the plant to go along.â

âGreat,â Frank answered. âAnd thanks. Weâll need only a day to get ready.â

âKeep me posted on developments,â said Mr. Allen, âand good luck!â

Only a few minutes passed before the telephone rang again.

âHello?â said Frank.

âThis is the ghost of Clint Hill,â an eerie voice announced. âI warn you, dead men tell no tales.â

Frank gripped the phone tighter. âWho is this?â

There was a moment of silence, then a loud burst of laughter.

âChet!â Frank exclaimed. âYou had me fooled.â

âYouâre speaking to a master impersonator,â Chet boasted.

Suddenly Frank was struck with an idea. âListen, pal, your ghost imitation may come in handy. Howâd you like to fly down to Ile de la Mer with Joe and me?â

âCount me in!â Chet responded excitedly. âJust make sure thereâs enough food aboard!â

The next day the brothers went to the Morton farmhouse to give Chet more details concerning the trip. They found IoIa Morton, Chetâs pretty, dark-haired sister, and Callie Shaw, an attractive blonde, seated in the living room. Callie was Frankâs favorite date, while Joe liked Iola very much. Standing in the middle of the room was Chet. He was whistling âHigh Journey.â

âHi, fellows!â he called, interrupting his performance long enough to take several bites out of the massive sandwich he was holding.

âHi!â Frank and Joe grinned as they took seats near the two girls.

âAs you can see,â Iola said with a smile, âChet is probably one of the best-fed ghosts in the business.â

âI need all the energy I can get,â Chet defended himself. âI might even start my own ghost-to-ghost network!â

By this time he had finished his sandwich, and hurried to the kitchen. Seconds later, he reappeared holding a large roasted turkey leg. Using it as a baton to mark the tempo, he resumed whistling.

âWhat if the real ghost gets mad at you for imitating him and decides to haunt you?â said Joe, chuckling.

Chet stopped whistling. He paled slightly. âUh, come on, fellows,â he quavered. âYou donât think Clint Hill is a real ghost, do you?â

âWe canât say for sure,â Frank answered, trying to act solemn. âAfter all, weâve never seen him. Weâve only heard him speak.â

Chet suddenly found his turkey leg unappetizing. He laid it down on a plate. The girls began giggling.

âThis is no laughing matter,â he said with a frown. But suddenly his expression brightened. âI know what Iâll do if Hill is a ghost! If he tries to scare us, Iâll scare him right back!â

Chet dashed from the room. Moments later he reappeared, his stout form draped in a white sheet. The others roared with laughter as Chet leaped playfully about the room with the sheet swirling behind him.

âBetter watch where youâre going!â Frank warned the cavorting phantom.

Chet now spread his arms wide under the sheet. Looking like a huge white bat, he took a high running jump across the room. Coming down hard, he tripped on one corner of the sheet. Chet lost his balance, stumbled, then fell and rolled across the room in a tangled mass of cloth. The girls joined in the Hardysâ fresh outburst of laughter.

âWhatâs so funny?â Chet groaned as he struggled to free himself. âI thought I looked pretty scary.â

âIf Hillâs ghost ever saw you in that get-up,â Frank said, âheâd laugh so hard he wouldnât be able to haunt anyone.â

Chet finally extricated himself and plunked down into a chair with a disgruntled expression. Just then Mrs. Morton appeared and invited everyone to have lunch. As they all ate, the three boys discussed the trip to Ile de la Mer,

âWish I were going,â Iola said wistfully.

A little later Chet accompanied the Hardys to the airport so they might check the plans for the trip. As they approached the Stanwide hangar, the boys spotted a twin-engine amphibian aircraft parked on the macadam ramp in front of the building. As they walked up to the craft, Jerry Maddenâs head suddenly popped from a window in the cockpit.

âHello, fellows!â he called. âHow do you like her?â

âA beauty!â Joe responded as they all admired the craftâs graceful lines and bright painted surfaces.

Jerryâs head vanished into the cockpit. A moment later a door opened in the side of the fuselage and he reappeared.

âWe just finished installing the long-range tanks,â Jerry announced. âAs it stands now, we can make Ile de la Mer nonstop and still have a couple of hoursâ fuel in reserve.â

âWhat about the return flight?â Frank asked. âWonât we have to refuel?â

âAccording to Mr. Allen,â Jerry explained, âthe exploratory team he sent to the island took a sizable supply of aviation gasoline with them. It was stored in 55-gallon drums. Some of them may have been unloaded and might still be there. However, if we find itâs goneâor is unusableâthe company will have more fuel flown down to us.â

After finding that everything was in roadiness, Frank said he thought they should plan to depart as soon as practicable. âTonight, maybe?â

âOkay!â Jerry replied. âIâll give the plane a final check, then see what the weather bureau will give us in the way of a route forecast. It would be good to leave tonight. Then weâd arrive at the island after sunrise tomorrow.â

The boys hurried off to make final preparations. The Hardys dropped Chet at his house, telling him they would return within a couple of hours. After arriving at their own house, Frank and Joe learned that their father had gone out of town.

Mrs. Hardy and Aunt Gertrude began preparing a substantial supper for the boys while they packed some light luggage. The two women tried hard to conceal their apprehension, but it showed on their faces. The boys assured them everything would be all right.

Finally they departed for the airport, picking up Chet on the way. As they walked toward the Stanwide hangar, the boys spotted Jerry Madden standing near the airplane. There were two men with himâtall, muscular fellows who appeared to be in their late twenties. The pilot introduced them as Bill Vogel and Kurt Lerner, the men Mr. Allen had selected to go on the trip. Bill and Kurt greeted the boys with hard, firm handshakes.

âWow!â Chet whispered as he straightened out the fingers of his right hand. âIâm glad those two are on our side.â

Soon everyone was aboard the amphibian and the engines were started.

âHow is the weather forecast?â Frank asked Jerry as they waited for the motors to warm up.

âExcellent!â Jerry replied. âHowever, there is a strong low-pressure system situated southwest of Ile de la Mer. It could develop into quite a storm center. Right now, itâs hard to say in just what direction it may move. But at present it shouldnât give us any trouble.â

He told the boys that once out of the continental United States, he would have to ask for Defense Visual Flight Regulation. After scanning the instrument panel methodically, Jerry picked up the microphone and communicated with Bayport tower. He asked for taxi and take-off instructions, and requested that his DVFR flight plane be activated.

Upon lining up the craft on the active runway to which he was cleared, Jerry eased the throttles ahead to maximum power. After a short run, the plane lifted off the ground easily. Jerry pulled up a small lever, which retracted the wheels into the fuselage.

When he reached the selected cruising altitude, Jerry set the plane on course. Hour after hour passed as it bore through the sky. Lulled by the drone of the engines, the boys caught up on some sleep.

When they awoke, the first light of dawn was breaking in the east. Gradually the light grew brighter, revealing a fascinating mosaic of deep blue and jade green on the surface of the ocean below.

âHow long have we been flying over water?â Frank asked.

âQuite some time,â Jerry replied. âWe left the United States coast about three hours ago.â

âYou must be tired,â Frank said.

âNot really,â Jerry responded. âI slept most of yesterday. Also, the automatic pilot gives me a chance to stretch my arms and legs once in a while.â

Chet had wasted no time looking into the food supplies for breakfast. The meal, consisting mostly of fresh fruit, was divided among the group.

âWe must be getting close to Ile de la Mer,â Jerry told the boys. He examined his chart closely. âOf course Iâm basing that on dead reckoning, which is not always as precise as we would like it to be. But do you see those cumulus clouds ahead?â

The boys nodded.

âClouds like that generally form over patches of land, such as an island,â Jerry said.

He maintained his course. Gradually the irregular outline of a small island loomed on the horizon.

âThatâs Ile de la Mer!â Jerry exclaimed. âIâve seen aerial shots of it that Clint Hill sent to Mr. Allen. It has a particular wedgelike shape which is unmistakable!â

He eased the nose of the plane down and descended to a lower altitude. Then Jerry aimed at the island and approached it at treetop height. Zooming in over the rocky coast, he pulled the nose of the plane sharply upward and followed the contour of the hills inland.

âThere doesnât appear to be any level terrain to land on,â he observed.

âNothing suitable along the coast?â Frank asked.

âMuch too rocky!â Jerry responded. âWeâll have to make a water landing.â

The pilot searched the coastline for a cove or inlet that would shelter the plane from the rougher waters of the open sea. Finally he spotted a small cove on the south side of the island.

Carefully studying the surface conditions, Jerry approached the cove and flared out several feet above the water. He now eased the throttles back and let the hull of the plane settle into the water. Taxiing into the cove, he called for the anchors to be heaved, then shut off the engines.

âThe island looks deserted,â Joe commented.

âJust the same we had better be careful,â Frank warned. âMembers of the gang could be in hiding somewhere.â

Jerry assured himself that the aircraft was secured firmly, then he inflated a large rubber raft to take the group to shore.

âIâm sure I can find the old campsite of the exploratory team,â Jerry said. âMr. Allen described it to me in detail.â

The Hardys, Chet, Kurt Lerner, and Bill Vogel followed the pilot through the thick trees and brush. Luckily it was not long before the group broke out into a clearing. There they found a small wooden shack, various pieces of machinery, and a number of 55-gallon drums marked âAviation Gasoline.â

Chet and Jerry examined the fuel supply, while the Hardys, accompanied by Bill and Kurt, went into the shack. They found it to be in good condition, and cans of food were stored on shelves along one wall.

âBy the looks of things here,â Frank observed, âIâd say this place has been occupied recently.â

The boys scrutinized the interior closely for clues to the occupant but saw nothing unusual. Then Joe noticed something white sticking out behind a row of cans on the top shelf. He reached up and pulled down two large folded sheets of paper. As he unfolded them, his eyes widened with excitement.

âFrank!â he exclaimed. âTake a look at this!â

Joe pointed to his discovery. âPlanning charts for aerial navigation! And here are course lines drawn on them!â

Frank dashed outside to summon Jerry and Chet. The pilot examined the charts with avid interest.

âThe course lines start at the exact latitude and longitude of this island,â Jerry declared.

He traced the line with his finger. It ran off the first chart, and continued on the second. The course led back into the United States to the approximate location of the camouflaged cave the Hardys had discovered. From there, it went to a point in a sparsely settled region of Montana.

âHow do you figure this mystery?â Jerry asked.

Frank answered. âThe gang must have been operating between the cave and this island. After we discovered the cave and things got hot for them, they decided to establish a new hideout in Montana.â

âLetâs go there!â Joe exclaimed.

Even Chet was enthusiastic about the idea. âMaybe Iâll still get a chance to play ghost!â

âCan the plane make it to Montana nonstop?â Joe questioned.

âWith full fuel tanks, and favorable winds, we can make it at least most of the way,â the pilot replied. âWe may have to stop once to refuel.â

Suddenly they all became aware that a strong wind was building up. Jerry ran out of the shack and scanned the sky. A dark, threatening layer of clouds was moving toward the island.

âThat storm center I told you about!â he shouted to the others. âIt has started movingâand itâs coming right across this place!â

The storm now seemed to be approaching with increasing speed. The winds grew stronger, and intermittent droplets of rain began to pelt the area.

âQuick!â Jerry ordered. âLetâs get back to the plane! Those anchors wonât hold in a big storm!â

Followed by the Hardys, Chet, and the two Stanwide men, he ran off into the brush and back along the path over which they had come.

The wind became more violent and the rain was falling steadily. It quickly increased to a heavy downpour which stung the faces of the boys and their companions.

Reaching the cove, the group leaped into the raft and started paddling toward the plane, which was already being tossed around like a cork. Despite all their efforts, progress was slow. Each stroke of the paddles took the raft only a few inches ahead.

Finally, they managed to reach the plane. Jumping onto it from the raft was a precarious operation. The craft rolled and pitched violently under the pounding of the waves.

The Hardys glanced at the anchor ropes anxiously. They were being strained taut.

âThose ropes will snap any minute!â Frank thought fearfully.

CHAPTER XIX

Hideout Trap

THE storm had now become a raging fury. Huge waves crashed against the hull of the amphibian, causing it to heave violently.

âThose anchor ropes arenât going to hold!â Jerry yelled.

âWhat about putting out more lines?â suggested Frank.

âWe have extra rope aboard,â said the pilot, âbut what do we attach it to? We havenât any more anchors.â

âI can carry the other ends of the ropes to shore in the raft and tie them to the rocks,â Frank replied.

âToo dangerous!â Jerry shouted above the wind. âThe raft would be swamped in a sea like this!â

âWe have no choice,â Frank answered. âWeâll have to take the chance.â

Frank worked his way aft and picked up two coils of rope. Joe and the others pitched in to help. Climbing outside and clinging to the heaving fuselage, they fastened one end of a coil of rope to the tail, the end of the other to the bow.

Carrying both coils with him, Frank jumped into the raft and began paddling toward shore, feeding out lengths of rope behind him. The raft pitched violently in all directions. Then suddenly a towering wave crashed over the young detective. The paddle was yanked from his hand and the raft turned over.

âFrank! Frank!â shouted Joe.

Suddenly his brotherâs head bobbed up in the tossing sea. He still clung to one of the ropes. Joe and the others grabbed it at their end and began hauling him in. As Frank neared the hull, another wave hit and slammed him against the plane. Although dazed by the blow, he continued to cling to the rope. Finally he was hauled aboard. They all climbed back inside the airplane.

âGood try, Frank!â said Kurt Lerner.

âToo bad I got swamped.â

âWhatâll we do now?â Joe asked as he felt the plane lurch hard against the anchor ropes.

âI have an idea!â said Jerry. âItâs our last chance!â

Scrambling forward, he strapped himself into the pilotâs seat. There he pumped the throttles a few times, worked the fuel primers, and turned on the engine ignition switches.

âWhat are you going to do?â Frank asked.

âTry to meet the storm on its own terms!â Jerry said grimly. âIf we can get started, I can head into the wind and try to ride it out!â

He engaged the engine starters. The propellers turned slowly, but the engines failed to respond.

At that instant a series of massive waves spilled over the plane. The craft heaved violently, snapping first one anchor rope, then the other. The plane began to drift rapidly toward the jagged rocks on shore.

Jerry continued to work the starters, but the engines would not respond! âThe ignition harnesses must be wet!â the pilotâs voice held a note of helplessness.

Chet looked out. The rocks were getting closer! âWeâll be smashed to pieces!â he yelled, taking a deep breath.

Frank rushed forward and climbed into the seat beside Jerryâs. Frantically he tried to help with the starting procedure.

âWeâd better get ready to jump overboard!â Jerry declared as he glanced at the deadly rocks looming up in front of his window.

Frank and Jerry continued to work the throttles and engage the starters. Suddenly the right engine backfired a few times, then burst into life.

Using the one engine, Jerry swung the plane around and headed into the wind and oncoming waves. By applying full power, he was able to halt the craftâs drift toward the rocks.

âThat was close!â Frank said, sighing in relief.

âWeâre not out of this yet,â Jerry said. âWith only one engine running, we have to apply so much power to hold our position that weâre likely to burn out the motor!â

He again tried starting the left engine. Finally his persistence paid off. The engine backfired once, then roared in response.

Jerry eased the throttles ahead and pulled still farther away from the rocks. He reduced power sufficiently to hold their position, yet prevent the engines from overheating.

âGreat job!â said Frank, and Jerry gave a wry smile.

The waves continued to batter the plane. Water seeped in through seams around the windows and the door, making it necessary for the occupants to bail constantly.

âHow can the plane take this pounding?â Frank asked.

âItâs a strong ship,â Jerry answered. âAlso, the fact that weâre in a cove is helping to take some of the kick out of the waves.â

The wind and the rain continued to rage. Jerry glanced at the fuel gauges.

âIf this storm doesnât end soon,â he observed gloomily, âweâll run out of fuel. Then weâll really be in trouble!â

Gradually, however, the rain and gusts of wind seemed to diminish in activity.

âI think the storm is moving off!â Joe said happily.

âYouâre right,â Jerry agreed.

As night fell, the rain stopped and the wind subsided to a gentle breeze. Switching on the planeâs bright landing lights, the pilot carefully taxied to a narrow part of the cove. Retrieving the rope which they had attached to the bow of the plane, Frank and Joe swam ashore and tied the end around a rock. Meanwhile, Lerner and Vogel had tied the stern line to another rock at the opposite side of the cove.

Satisfied that the airplane was now secure, the whole group fell exhausted on the beach and slept soundly through the remainder of the night.

The next day, after a breakfast from the planeâs store of provisions, Jerry began an examination of the craft for damage. The Hardys, with Chet, Lerner, and Vogel, set out to collect the drums of aviation gasoline. It was long, arduous work. Each of the drums had to be rolled through the brush to the shore of the cove, loaded onto the raft, which had washed ashore undamaged, then ferried to the plane. There the contents were emptied into the fuel tanks.

It was late afternoon before the refueling operation was completed. The boys then made a quick tour of the small island, but found no one hiding there. Jerry, meanwhile, had examined every inch of the plane and reported it to be airworthy.

âI suggest we take off immediately, while we still have some daylight,â he said.

Soon they were airborne again, headed for Montana. They flew throughout the night. Shortly after daybreak, Jerry landed once to refuel, then set off again. By late morning he announced that they were over Montana.

âIâll head for the area indicated on that chart you boys found on the island,â said the pilot.

When they reached it, he established a search pattern by maneuvering the aircraft into a series of weaving courses. The boys looked with fascination at the twisting valleys and rivers below. Mountains jutted up all around them.

âExactly what is it weâre looking for?â Chet questioned.

âThe gangâs hideout would have to be near a long, level stretch of ground which could serve as a runway,â Frank answered. âThis particular area is rugged, so there canât be too many spots for landing.â

Jerry applied more power and climbed to a higher altitude to clear some of the lower mountains. He continued the search pattern.

âItâs like looking for a needle in a haystack,â Chet mumbled.

âWait a minute,â said Frank. âLetâs take a closer look at that spot over there.â He pointed slightly to his right.

Jerry rolled into a turn and straightened out in the direction Frank had indicated.

âSee the timber line on the side of that mountain ahead?â Frank asked. âThereâs a stretch of level ground right above it.â

âI see it!â Joe exclaimed. âAnd say, thereâs a shack in a clearing in those woods about half a mile away.â

The pilot also sighted the spot. He maneuvered the plane closer to the level area.

âWhat do you think?â Frank asked Jerry.

âItâs level enough and plenty long for a landing. Iâd say it would make an ideal runway. And that grove of trees at the far end would be a perfect hiding place for an airplane.â

Frank suggested that they land and investigate the area. Jerry headed the plane down and flew at a height of less than a hundred feet above the ground.

âThe surface looks smooth,â he said. âIâm going to swing around and make a long approach for a landing.â

He rolled the plane into a turn and then lined it up with the level stretch of ground, reduced power, extended the landing gear, and lowered full flaps. The craft touched down smoothly and rolled to a stop with plenty of room to spare. Jerry taxied toward the grove of trees, shut off the engines, and parked. The Hardys, followed by the others, got out and glanced around at the hard, bare ground.

âIt doesnât look as if anyone has been here before,â Frank remarked glumly.

âI guess weâre just on a wild-goose chase,â Joe said with a frown.

âHey, fellows!â yelled Chet, who had been reconnoitering an area that sloped away from the grove of trees where the ground was softer.

Frank and Joe rushed over to their chum.

âLook!â Chet said, pointing at the ground. âFootprints!â

All the boys examined the tracks closely. The heavy impressions of a manâs shoes were clear, and led down the slope. âThe prints were made recently!â Joe concluded.

Excitedly the young detectives followed the trail of prints. Lerner and Vogel tagged along a short distance behind. Jerry Madden remained with the plane.

Suddenly Frank stopped and gazed straight ahead. He gestured for everyone to be quiet. Through the trees they could see a small shack.

Motioning Joe to follow him, Frank began to creep toward it. Reaching the shack, the boys peered through a knothole in the wall. What they saw startled them. Seated inside were Lance Peterson and Aaron Lieberl Tensely the Hardys each pressed an ear to the wall in hopes of overhearing the menâs conversation.

âWhy should we divide the loot equally?â the boys heard Lieber growl. âWe did most of the work.â

âWeâll only divvy up what weâve already unpacked,â Peterson replied. âThe stuff we buried in the old dry well wonât be missed by the others. Weâll keep that for ourselves.â

âThe rest of the guys ought to be flying in soon,â Lieber said.

This remark startled and worried the boys. They must hurry to capture these men before the new arrivals might capture the Hardys and their companions!

When the brothers reported what they had heard, Lerner and Vogel offered to rush the place and seize Peterson and Lieber.

Frank did not agree. âThey may be armed,â he said. âBy the time we broke into the shack, theyâd have a chance to use their weapons. Letâs get them to come outside.â

âHow?â Joe asked.

Frank grinned at his brother, then turned to Chet. âHereâs your chance to play ghost.â

Chet and the Hardys hid behind some brush located a short distance from the shack. Vogel and Lerner took up concealed positions nearby.

âOkay.â Frank quickly whispered something to his stout friend. âYouâre on.â

Chet cleared his throat, then called out in deep, eerie tones:

âThis is the ghost of Clint Hill! You cannot escape a man that you have killed!â

A second later Peterson and Lieber bolted from the shack. Terror-stricken, they looked around.

âThe ghost! Itâs the ghost!â Peterson screamed. âWeâve got to get away!â

Lerner and Vogel sprang out from a bush. Leaping on the two thieves, they quickly overpowered them.

âWhatâwhatâs going on?â Lieber shouted, dumfounded.

The captured men were even more startled to see the Hardys striding toward them.

âWhat are you two doing here?â Lieber yelled.

âHow did you find us?â blurted Peterson. âAnd whereâs the ghost?â

âNever mind,â said Frank. âWho else is in the gang with you?â

âWeâre not talking,â growled Lieber.

âIf you wonât tell us, weâll find out anyway,â said Frank. âBush Barney and Anchor are in jail. We know some more of your pals are due here shortly.â

The prisoners glanced at each other apprehensively. They were herded into the shack, seated in chairs, and their hands tied firmly behind their backs.

Frank said that he and Joe would guard the two captives. He instructed Lerner, Vogel, and Chet to go back and warn Jerry that more members of the gang were flying in.

âMake sure our own plane is hidden,â Frank commanded. âThen wait there and nab whoever arrives.â

Alone with Peterson and his henchman, the Hardys began to question them. Peterson offered to make a deal, but the boys refused to listen. The only concession Frank would make was that it might go easier for the men if they would cooperate.

That seemed to make up Petersonâs mind. âI can give you a complete list of everybody whoâs in this with us,â he said, âand how the whole operation worked. Youâll find it all in that metal box up there on the top shelf.â He nodded toward the opposite end of the room.

Frank walked over to the shelf Peterson had indicated. He looked up at the box. It was not very large, but difficult to reach.

âIâll give you a hand,â Joe said, coming over.

They stepped closer and began lifting the box. The next instant there was a click, and suddenly the floor beneath their feet gave way! A trap door! The boys plunged helplessly into a dark hole. Landing with a thud on soft ground some ten feet below, the Hardys scrambled up just as the door slammed shut above them. At once they became aware of a hissing sound in the darkness.

âWhatâs that odor?â Joe asked frantically.

âIt must be some kind of gas, Joe!â

In the room above they heard the two men break into raucous laughter. As the hissing sound continued, the boys realized with horror that they were losing consciousness!

CHAPTER XX

Runway Victory

MEANWHILE, Chet and the two men had arrived back at the plane. Jerry was amazed to hear that Peterson and Lieber had been captured.

âAnd more members of the gang are expected to land here at any time,â Chet added. âFrank says to hide the plane.â

âWeâd better push it under the trees,â Jerry said.

Together, they rolled the aircraft deep into the little grove. Then they watched the sky and waited.

âI hope there arenât too many of them,â Chet said nervously.

Nearly an hour passed before the droning sound of an airplane was heard in the distance.

âThere it is!â Jerry shouted. âLetâs take cover!â

They watched the craft as it circled and headed in for a landing. The pilot set the plane down gently, then taxied toward the grove. The plane came to a stop and three men climbed out.

âOne of those men is Rodax,â Vogel whispered. âHe worked at the Stanwide plant.â

âAnd Iâve seen the short guy around the plant too,â added Lerner. âNameâs Ungerâheâs one of the shipping clerks.â

Neither he nor Vogel recognized the third man, who had piloted the plane.

âI donât recognize him, either,â said Jerry.

The three men started walking toward the trees. When they sighted the amphibian, they came to an abrupt stop.

âI didnât know we had another plane working with us,â Rodax was heard to say.

The men walked forward for a closer look.

âLetâs get them!â Chet whispered.

He and the others leaped on the thieves. Rodax and his companions were caught completely unawares. They were quickly subdued, almost without a struggle.

âWhat is this?â bellowed Rodax.

At that instant Chet had an idea. He realized that Rodax and the other two henchmen had never seen him before. However, they did recognize Jerry Madden, Lerner, and Vogel as employees of Stanwide. Perhaps if the thieves were led to believe that Peterson and Lieber had talked them into coming in on the deal without their confederatesâ knowledge, it might make Rodax and the others angry enough to talk.

âYou might call it a double cross!â Chet said.

âDouble cross? What do you mean?â Rodax demanded.

The man Lerner had recognized as the shipping clerk appeared greatly alarmed.

âMaybe Peterson has brought these guys in on the deal,â he said, âand plans to push us out!â

âIs that right?â Rodax shouted angrily.

âWhy donât you ask Peterson and Lieber about that?â Chet taunted with a grin. âAsk them about the littleâerâagreement we made with them.â

Jerry and the others quickly caught on to what Chet was trying to do, and played along.

âIf those guys did double-cross us, itâll be just too bad for them!â shouted Rodax. He was now in a furious mood.

The three thieves were marched off to the shack. As they approached, Peterson and Lieber, who had freed themselves from their bonds, came running out the door.

âIt must be true!â growled Rodax. He leaped toward Peterson with clenched fists and knocked him to the ground. The shipping clerk rushed at Lieber. The pilot did not attempt to join in, but merely stood watching nervously.

âLet them fight it out among themselves!â yelled Chet. Concerned about the Hardys, he ran into the shack. âFrank!â he called in a worried voice. âJoe!â

Chet rushed outside.

âJerry!â he cried out. âFrank and Joe are gone!â

Exhausted from their violent struggle, the four thieves painfully got to their feet.

âWhat has happened to the Hardys?â Chet demanded angrily.

Peterson and Lieber remained silent.

âLetâs tie them up!â said Jerry.

Peterson and the others were taken into the shack, firmly bound and seated in chairs.

Chet searched the room. He was in a frenzy.

âYouâd better tell us where the Hardys are,â Jerry said angrily, addressing Peterson and Lieber. âOtherwiseââ

Still the men refused to speak. The strange pilot, who had been getting more nervous by the minute, finally broke down.

âI was dragged into this racket!â he yelled. âI donât want to go to jail! Iâll turn stateâs evidence!â

âWhatâs your name?â Chet asked him.

âKyle Rodney,â he responded. âAnd Iâve been in this shack before. They have a trap door in the floor, over by those wood shelves, with a special catch that automatically releases when anyone steps on the door. Lieber designed it that way, in case snoopers did come here. Before stepping on it himself, he locked it. Your friends are probably down below.â

âShut up!â growled Lieber.

Chet, with the aid of Lerner and Vogel, pushed hard on the trap door. It swung downward. âI smell gas!â Chet exclaimed.

âItâs harmless,â Lieber said. âWhen the trap door opens, it uncorks a bottle rigged to the underside.â

Chet peered into the hole. âThere they are!â he shouted. âTheyâre unconscious!â

âOnly asleep,â Peterson put in. âThat gas wouldnât hurt anybody.â

Chet grabbed a length of rope, handed one end of it to Lerner and Vogel, then lowered himself to where Frank and Joe were lying. He quickly looped the rope under Frankâs arms, and called to the men to haul the young sleuth up. Then it was Joeâs turn.

The boys were carried outside the shack. After several minutes in the fresh air, the Hardys began to regain consciousness.

âWhat happened?â Frank murmured in a weak voice.

âYou and Joe fell through a trap door in the shack,â explained Chet. âSome kind of gas was released that knocked you both out.â

âOh, yes, I remember now,â Frank said, holding his head. Then he sat bolt upright. âHowâs Joe?â he asked.

âOkay,â Chet assured him. âHeâs just a little groggy. Lucky that gas wasnât deadly!â

Within a few more minutes the boys had fully recovered. They went into the shack and questioned their prisoners.

âWhy did you steal Clint Hillâs airplaneâthe one we found in the cave?â Frank asked.

The captured men glared at the young sleuth in silence.

Frank decided to play a hunch. âThat hoist in the planeâyou used it to transfer the stolen goods while in flight, didnât you?â Slyly he played on Petersonâs vanity. âI have to hand it to you. That was some trick! How did you manage it?â

âIt was simple! I got the idea after watching some newsreel films on air-to-air refueling,â Peterson boasted. Too late, he realized that he had been tricked into confessing. With nothing further to lose, he began to spell out the details of the scheme, as if wanting the boys and their friends to admire his cleverness.

âI stole Hillâs plane to use in the operation, and we rigged a hoist to it. When we planned a job, Iâd arrange to fly the shipment at night so we wouldnât be seen. Then Kyle Rodney, in the hoist plane, would rendezvous with me over some predetermined point, lower a light cable, and weâd transfer a few boxes of platinum parts from the Stanwide plane to his.â

âI had to do it!â exclaimed Rodney. âPeterson found out that I had once been in trouble with the law and served a prison term. I was afraid Iâd lose my pilotâs license!â

âYour hoisting operation was pretty risky, wasnât it?â Jerry asked.

âIt was the only way,â Peterson confessed. âIf I had had to land the cargo plane to unload the stuff, the delay would have shown up on my flight plan. That would have been a dead giveaway.â

Lieber stared at Peterson. He was flushed with anger at his partnerâs betrayal.

âAfter the air-to-air heist,â continued Peterson, ignoring him, âRodney would fly the stuff to our cave hideout. Bush Barney and Anchor would then set up a roadblock to prevent motorists from using the road near the cave, for fear they might see the plane land in the pasture. If a motorist ignored the roadblock, they would set off flares to warn Rodney not to come in.â

âSo it was you who hit our car with the wheels of your plane the night we drove along the road!â Frank said accusingly to Rodney.

âThat was an accident,â Rodney answered. âBush Barney was late in lighting the flare, and I was too low to pull up and go around.â

Peterson then asked the Hardys a question. âHow did you learn about this hideout?â

âThat was easy,â Frank replied. âWe found an air chart on Ile de la Mer with a course to this place marked on it.â

âYou fool!â Lieber bellowed at Peterson. âWhy did you have to forget that chart!â

âWhat were you doing on Ile de la Mer?â Frank asked Peterson. âDid you hide any loot there?â

âNo,â Peterson responded. âWe had planned to use it as a hideout. But then we changed our mindsâwe were afraid Mr. Allen might decide to send another exploratory team there.â

âBunglers!â mumbled Rodax.

âThen I remembered this spot,â Peterson continued. âMy grandfather used to bring me hunting here when I was a kid. I thought it would make a perfect hideout. We high-tailed it from Ile de la Mer so fast that I forgot to take the chart I had plotted the flight on.â

âWho threw the hand grenade at us?â asked Joe angrily, remembering their close call in the Stanwide hangar.

âThat was Rodax,â Peterson said quickly, eager to disclaim responsibility for the brutal attack. âAnd it was his idea to get you boys to my office so he could have Lieber steal your camera and films from the plane. Youâll find the camera in a Bayport pawnshop.â

âShut up!â shouted Rodax.

Joe, taking a guess, said, âZimm, too, worked with you. He spied on us, and covered Clint Hillâs prints in the hangar in case he was still alive and we might trace him. Also, Zimm tried to drop that hunk of machinery on us in the warehouse.â

âYes,â Peterson replied.

Frank turned to Lieber. âYour brother-in-law is innocent, isnât he? You just used him for a dupe?â

âYes.â

The Hardys asked Peterson the location of the dry well where he and Lieber had hidden the loot that they intended keeping for themselves. On hearing this bit of treachery, Rodax and the shipping clerk were ready to tear Peterson and Lieber apart.

Frank whispered to Jerry Madden that he should summon the State Police on the planeâs radio, and also request them to relay word to Bayport Police Headquarters to have Zimm arrested. The pilot left the shack. A few minutes later he returned and nodded to the young sleuth that he had been successful.

Before long, a large Montana police helicopter arrived and the thieves were taken into custody. As Peterson left, he stopped for an instant and turned to the boys.

âRemember,â he said threateningly, âClint Hillâs ghost is still on the loose! You never solved that mystery!â

âNo, but we mean to learn the truth,â Frank answered, and added, âYou left a note to Lieber in that cabin saying the ghost knew too much, didnât you?â

âYes, I got a lot of radio messages that wereâerâtoo revealing. They came over my office set that was always tuned to unicom.â Peterson would not explain any further.

When the Hardys and their friends returned to Bayport, they received a joyous homecoming. Mr. Allen was overwhelmed by the sleuthing ability of the boy detectives. Frank and Joe refused to accept the handsome check he offered them, but said that their friend Chet would settle for the biggest meal he could find in Bayport!

Two days later the brothers received a telephone call from Mr. Allen, asking them to come to his office. When they arrived, his secretary looked at them with a big smile.

âGo right in,â she said.

As the boys opened the door to Mr. Allenâs office, they were astounded to hear someone whistling âHigh Journeyâ!

âCome in!â said Mr. Allen as he rose from behind his desk. He nodded toward a bearded young man at the end of the room. âMeet Clint Hill, boys!â

The Hardys stood speechless for a moment, unable to believe their ears. Clint Hill shook hands with them, then after they all sat down, he began to relate his story.

âAs you know, Peterson and I and our passengers crashed at sea during a return flight from Ile de la Mer. After we hit the water, the three mineralogists drowned almost instantly. Peterson took the one available life raft and left me clinging to the wing of the plane. I was slightly injured and couldnât swim after him.â

âWhat did Peterson hope to gain by abandoning you?â Frank asked curiously.

âAs he paddled off in the raft, he shouted to me that now he would become chief pilot of Stanwide. And that he would fix Mr. Allen. Then I fainted. I must have unconsciously clung to a piece of wreckage, because the next thing I knew I was on an island, being cared for by some natives. They spoke only their own language, which I couldnât understand.â

âLucky the natives were friendly,â Frank said.

âOh, yes,â Clint replied. âAfter I recovered, they took me to another, bigger island in a dugout canoe. It was there that I managed to get a job and earn enough money to buy boat passage back to the United States. I decided to keep my identity a secret and stay in hiding until I found out what Peterson was up to. I didnât even get in touch with Mr. AllenâI wanted to be sure of my ground before making any accusations.â

âWhen did you decide to become a ghost?â asked Joe, grinning.

âI knew Peterson was superstitious,â the pilot said, âso I got a job with the ground crew at a field near Bayport. I began to bug him with the ghost business, hoping to make him confess not only that he had left me to die, but what he was doing to âfixâ Mr. Allen.â

âGreat idea!â Frank said with a chuckle. âIt even had us worried for a while. I guess Peterson asked us to work for him to throw us off the track. By the way, was it you who wore a mask one night at Zimmâs house and gave me a punch?â

âWas that you?â Hill asked, embarrassed. âIâm sorry. I thought it was one of Petersonâs pals!â

âNo harm done.â Frank grinned. âGo on with your story.â

âAfter Iâd been here a while,â Clint continued, âI took the airport operator I was working for into my confidence. He allowed me the use of an airplane to do some investigating, and I succeeded in tracking Peterson to Anchorâs cabin, but I couldnât find the cave. I see you boys did, though! And when he skipped, I phoned your house to find out where heâd gone. But you tried to bargain with me and of course I couldnât do that.â

âNo.â Frank laughed. âOf course you couldnât.â

The young pilot congratulated the Hardys on the fine job they had done in uncovering Petersonâs scheme against Mr. Allen. The boys felt gratified, but longed to solve another mystery. It was to come as they worked to find out the riddle of a story about What Happened at Midnight.

Mr. Allen heartily echoed Clint Hillâs praise. âAnd since you Hardy boys are the best sleuths in the business,â Mr. Allen added, âyouâve probably figured out that you are now looking at Stanwideâs permanent chief pilot! That is,â he added, with a grin in Clintâs direction, âif our ghost gets around to shaving off those whiskers!â