A door slammed. There was a short, silent wait. Then they heard a car engine running in the yard behind the store.

"Okay!" came Stark's voice. "Coast is clear!"

Frank and Joe were lifted up, carried a little way, then dropped on the floor of the automobile.

Tensely the two boys waited to hear police whistles and Chief Collig barking orders. But the car began to move, rolling swiftly out the alley, and away.

"What happened to our plan?" Frank wondered. "Where's Dad?"

"We must have gone in too soon," Joe thought, dismayed. "The police couldn't get here in time!"

As the car drove on, Frank and Joe recognized the sounds of heavy traffic all around them. Gradually the vehicle picked up speed. The engine purred steadily, and the tires whined along on what could only be open highway.

Presently the car swerved, b.u.mped over uneven ground a short distance, and stopped. In the sudden silence the blindfolded youths could hear the sound of surf on the beach.

"We're near the sh.o.r.e," Frank reasoned. "Shantytown perhaps. The time it took getting here seems about the same as when we came before."

The car doors were opened. Again the boys were lifted and carried. A minute later each of them felt a jarring pain as he was dropped on a wooden floor. Rough hands ripped away their blindfolds.

Although tightly bound, the Hardys struggled to sitting positions. They were in a small board shack. A little light came through a tiny window high up in one of the walls.

Ben Stark and Moran were going out the door. Stark looked back. "Keep your eyes open, Duke," he ordered sharply. "Those kids are slippery."

"Don't worry," the pale-faced man replied insolently.

After his two companions had left, he went to a water bucket in one corner, dipped in a tin cup, and drank thirstily. Then he sat down in a wooden chair and tilted back lazily against the wall.

Frank and Joe listened anxiously for sounds of rescue. They could hear the sea, but nothing else.

Carefully they looked over their prison. The shack was crudely built out of broken crates and old two-by-fours. Long, sharp points of nails stuck through the wall near Duke's chair. At the rear of the room was a little squat wood-burning stove.

Cramped and helpless, the boys could only wait. As night came on, Duke stood up and lighted a kerosene lantern hanging on the wall. Then he sat down and tilted back his chair again.

"Might as well face it," thought Frank. "Rescue isn't coming." He looked at Joe with silent urgency, and his eyes said plainly, "It's up to us!"

CHAPTER XV.

Outwitting a Suspect ALTHOUGH bound and gagged, the Hardys exchanged messages. Frank's glance slid to their guard, tilted back in his chair against the wall. Then he looked at his brother.

Joe nodded slightly to show he understood and looked toward the lantern. The gla.s.s was turning black with soot and the room was in deep shadow.

"Lucky it's dark in here," he thought, "because we'll have to get these ropes off without being seen."

Frank's eyes fastened on the long nails he had seen sticking through the wall near the chair legs. If only he could get his back to those sharp points I Cautiously he inched toward the wall. Duke, who appeared to be asleep, did not stir. Joe also moved.

Bit by bit, the brothers worked their way closer to the protruding nails.

At last Frank sat with his back against the wall, not far from the guard's chair. Hardly daring to breathe, he felt behind him until a tenpenny spike p.r.i.c.ked his wrist. If he was lucky, his scheme would work!

Frank eyed his captor. The man was still asleep. Quickly Frank rubbed the rope against the sharp point.

He could feel the strands separate, one at a time. His arms and back ached, but he kept on doggedly.

Finally the rope was severed. His hands freed, he removed the gag, then pulled out his pocket-knife and cut the ropes around his ankles. Reaching over, he cut Joe's bonds.

Then Frank seized a leg of Duke's tilted chair and jerked it out from under the guard. Slam! Duke fell on his back and cried out.

Frank and Joe leaped on him together, but he rolled away. As he bounced to his feet, Joe brought him down with a tackle.

Fighting desperately, the guard kicked, bit, scratched, and finally broke away. Gasping, he backed into a corner. As Frank went after him, Duke grabbed the kerosene lantern and hurled it. The boys ducked.

Crash! The gla.s.s shattered and kerosene drenched the opposite wall. A flame licked up the side of the shack.

"Water!" Joe yelled. "The bucket!"

He tore off his shirt and tried to beat out the flames. At the same time, Frank and Duke grappled for the pail. Duke jerked it away and flung it at Joe. The bucket narrowly missed him, slamming against the wall.

The water splashed over onto the flames with a hissing sound.

"You young fools! I'll get you for this!" Duke picked up the chair and raised it over his head. But Frank swung a right-hand haymaker. It caught Duke in the solar plexus and he went down in a heap.

"He's out cold!" Joe cried, whipped off his shirt, and finally smothered the flames. "What a sock that was!"

Duke moaned and stirred. Swiftly the boys felt around until they found the cut ropes. Panting, they bound their prisoner's hands and feet.

"That should hold him," said Joe as the boys stood up.

"Now, let's see where we are," Frank suggested.

Cautiously he opened the shack door and the brothers slipped outside.

"It's the edge of Shantytown," Joe whispered after a quick look around.

Across a whitish stretch of sand they could see the dark shacks and beyond them a red glare from beach fires. A nearly full moon sailed in and out of heavy clouds.

Suddenly a figure detached itself from the shadow of the shanties and glided quickly across the sand toward them. Fists ready, Frank and Joe set themselves for a fight!

"Put up your hands!" came a firm command. "You're under arrest!"

At the same moment, moonlight fell upon a familiar face. "Pat Muster!" Frank exclaimed joyfully. "Are we glad to see you!"

Pat Muster was a plain-clothes man on the Bayport police force. The brawny, red-haired man turned his flashlight on the bruised, disheveled boys. "So you fought your way out, eh?" he said, putting away his revolver. "Too bad you didn't yell for help. My men and I were staked out by the shacks, keeping an eye on this place."

Frank grinned ruefully. "I wish we'd known that. We didn't call out, because we were afraid of bringing more of the gang."

"Where's our father?" Joe asked.

"He took a squad of police and followed Stark and the other fellow. The chief went back to headquarters."

"I see," said Frank. "When you didn't close in at the store, we thought the plan had backfired."

"Your father suggested that we follow you, on the chance of locating the rest of the gang. Sorry I left you in the shack so long," he added. "I was hoping some more of these tough birds would turn up and we'd make a bigger haul."

"We have one of them for you," Joe said, "all trussed up and ready to go."

Pat Muster chuckled. "I've got to hand it to you, boys," he said. "You always deliver the goods!"

He turned toward the shanties and gave a low whistle. Here and there a half dozen figures appeared from the shadows and crossed to join the boys and Muster at the shack.

"Wait here," the officer ordered his men. He and the Hardys entered the shanty. The detective beamed his flashlight on the p.r.o.ne figure of Duke, who blinked and scowled.

"Now that you're awake," Frank said, "you'd be smart to tell us where our missing chums are."

The man glared and did not answer.

"Don't waste time on him," Joe advised. "Let's search this place. Maybe the bank loot is hidden here."

Frank and Joe borrowed flashlights from two of the men outside and began to help Detective Muster.

They inspected the crude walls and flooring. Finally, they stood up, disappointed.

"Nothing," Frank said, "and there's no other place to hide anything except in the little stove."

At this, Duke darted an apprehensive look at the stove. In two quick strides Frank reached it, lifted the stove lid, and plunged his hand inside.

"There's something here!" he exclaimed. He pulled out a limp object. "A rubber mask! I think there are morel" he added quickly, reaching in again. One after another, he brought out four additional false faces.

Joe whistled. "The bank robbers' masks! What a find! This shack must have been their headquarters-for a time, at least!"

"Great work, Frank!" Detective Muster congratulated him. "There'll probably be plenty of fingerprints on those masks." He pulled a large folded paper sack from his pocket and opened it. "Drop them in here."

The detective summoned two of his men to unbind the prisoner Then they handcuffed Duke and led him to the police cars hidden in the pines on the other side of Sh.o.r.e Road. Muster and the boys followed.

When they reached headquarters, Chief Collig sent the rubber masks to his lab for immediate fingerprint a.n.a.lysis. Finally he turned to the Hardys. "Letting yourselves be kidnaped was a daring stunt, boys. But you got results." He looked at Duke, who sat beside him, scowling.

Frank drew the chief aside and asked quietly, "How about Dad and his men? Have they located Chet and Biff?"

The chief shook his head. "They should have radioed in by now," he replied. "Let's see what we can get out of the prisoner." He walked over and stood in front of Duke. "If you know what's good for you-" he began but was interrupted by a clatter of feet outside.

The next moment Ben Stark and Moran, handcuffed together, entered the chief's office, followed by Fenton Hardy and two policemen. "Dad!" cried Joe. "Did you find Chet and Biff?"

"No," said his father quietly. "Are you boys all right? You look as if you'd had a rough time."

"We're okay," Frank a.s.sured his father quickly. "Tell us your story."

"We followed Stark and Moran from Shanty-town," his father explained. "They drove down to the docks and sat there, apparently waiting for a boat. When it didn't show up, they headed back to Shantytown.

So did we. As soon as I saw that Pat was missing from his station, I knew you boys and your guard had been brought here. We arrested these two right in the shack."

"Do Stark and Moran know where Biff and Chet are?" Joe asked.

"I think they know all right," Fenton Hardy said grimly. "But they're not talking."

Frank and Joe looked disappointed.

"Cheer up," Chief Collig advised them. "You've done a terrific job. We can hold these three on a charge of kidnaping you. After we've checked the prints on the masks you found, we'll probably be able to identify them conclusively as the bank robbers."

After the sullen prisoners were taken away. Frank and Joe told their father and the police what had happened to them. Then the Hardys left the station and piled into the detective's car.

"We'll pick up our motorcycles tomorrow," Frank said.

When they reached home, the three shared a late supper of cold chicken, milk, and apple pie. Then they went straight to bed.

The next morning, as the boys were coming downstairs to breakfast, the telephone rang. "I'll get it," said Mr. Hardy, picking up the receiver.

A few minutes later he joined the boys in the dining room. "That was Chief Collig," the detective announced. "The fingerprints of Ben Stark, Fritz Stark, Duke, and Moran-all wanted by the police-were on the masks. One set of prints is unidentified."

"They probably belong to the big bald fellow," said Frank. "The one Mr. Caine mentioned."

"Caine!" exclaimed their father. "In all the excitement I forgot to tell you that Mr. Caine phoned yesterday just after you left for the costume shop. He wants you to call him."

At this news the boys hurried to the hall and Frank dialed the long-distance call to Northport. In a few seconds Frank was speaking to the friendly dock manager.

"You remember those fellows who rented the Black Cat from me?" he asked. "Well, one of 'em left an empty envelope in his hotel room. I own the hotel, that's how I found it. Thought it might help you to track 'em down. Fritz Stark's address is on it."

"That's wonderful, Mr. Caine!" Frank cried out, and said to Joe, "He has what might be the Starks'

address." Turning back to the telephone, Frank asked, "Where was the letter from?"

"Let me see . . ." the dock manager said. "It's from Worldwide Radio Distributors, Yokohama, over in j.a.pan!"

CHAPTER XVI.

Skeleton Symbol "MR. CAINE," said Frank in a puzzled tone, "may I have the address on the letter?"

After jotting down the information, Frank thanked him and said good-by. He told Joe, "Just a San Francisco hotel. But the sender was the distributor for radios in Yokohama."