Joe nodded. "Then there's Ben Stark, the pilot of the Black Cat, which by the way, came down from Northport the day of the bank robbery. Is he linked with both cases? And is his pal Sutton? And where do the fights at Shantytown fit in?"

"That's for us to find out," Frank said determinedly. "Especially since the answer might lead us to Chet and Biff. We're pretty sure they were in Shantytown-since we found Chet's gorilla mask off the coast there, and his sleeve was picked up behind Sutton's shack."

The excitement suddenly faded from Joe's face. "Maybe our hunches are on the wrong track. After all, Fizzle could be sold in other places besides Northport-and we have no proof the bald guy left the bottle in the Sleuth"

"Don't be a pessimist," Frank begged. "Remember what Dad says: 'Persistence is just as important as cleverness in detective work.' "

"Yes, and a little luck helps, too. Don't worry. It's just that we have so many mysteries to solve. Which one do we tackle next?" The ringing of (the telephone interrupted. Frank answered.

"Glad to find you home," came Chief Collig's familiar voice. "Maybe you can help me. We have a man down here-been brought in for stealing. He seems to think you and Joe can clear him."

"Joe and I?" repeated Frank, astonished. "Why . . . what's his name? What does he look like?"

"He's a big, strong fellow-a stevedore. Calls himself Alt"

CHAPTER XI.

Midnight Caller "ALF Lundborg a thief!" Frank exclaimed. "I can't believe it! We'll be right down, Chief Collig," he promised.

"I don't buy it," Joe said flatly as they started out. "What's the pitch?"

Frank shrugged and hurried off to inform his mother of the errand, while Joe locked the laboratory. Then the brothers rushed downtown on their motorcycles to Chief Collig's office.

"Where's Alf?" asked Joe, looking around as he entered.

"We're holding him in a cell until I talk to you boys," the officer explained.

"He's the man we told you about yesterday," Frank reminded the chief. "The one who helped us in Shantytown. If it hadn't been for him, Sutton would have cracked my skull with a blackjack."

"I remember," the chief replied. "Sutton's the cause of his arrest." Before the surprised boys could speak, he added, "I'll let Lundborg tell you himself." Over his intercom he ordered the suspect brought in.

"I don't believe Alf's a thief," Frank said.

"But he does have a record for petty theft and disturbing the peace," Chief Collig said soberly. "That makes it look bad for him."

"How long ago was that?" Joe asked.

"Alf's last brush with the law was five years ago," Collig replied. "He claims he was just a wild kid at the time."

The door opened and Alf stood on the threshold. His giant frame almost hid the sergeant behind him.

When he saw the Hardys, his troubled face lighted up instantly.

"I knew you fellows wouldn't let me down," he burst out. "Tell the chief I didn't take it!"

"Take what, Alf?" said Frank.

"The police found a transistor radio in my knapsack," the big man explained, "but I didn't put it there!"

"Sutton reported it stolen," the officer said. "We sent out Lieutenant Daley to investigate, and he found it in Lundborg's bag."

"Is Lieutenant Daley still here?" Frank asked. "Would you have him come in?" Collig nodded.

A few minutes later a tall, thin-faced officer entered. He and the Hardys had known one another for years and exchanged greetings. "Lieutenant Daley," Frank said, "when you were hunting for the radio who suggested that you look in Alf's knapsack?"

"Sutton," the officer answered.

Frank nodded. "It looks like a plant, Chief."

"Sure it is," Joe declared. "Alf scared Sutton off when he attacked Frank. He probably planted the radio to get even."

"That's right! That's just what I told them!" Alf boomed. "Thanks a lot for sticking by me, fellows. I'll get Sutton!"

"Hold on there!" commanded Chief Collig. "You'll be back here for a.s.sault if you try that. Since the Hardys back up your story, I'll let you go. But if Sutton prosecutes, we'll have to bring you in again."

"Okay." Alf wrung the boys' hands, thanked them, and left.

Frank pointed to a radio on Collig's desk and asked, "Is this the stolen property?"

"That's it," Lieutenant Daley spoke up.

"Take a look," the chief invited, and Frank picked up the compact, heavy little set.

"j.a.panese make. Yokohama Super-X."

"Let's see," Joe requested. He gave a low whistle as his brother pa.s.sed it to him. "What a little beauty!

Brand new, too. Look at that nickel-and-ivory case!"

"It's an expensive, rare set," Lieutenant Daley commented. "Not many people can afford one."

"That's true," Frank said. "Hank Sutton seems to be just a seedy-looking character who lives in Shantytown. But Joe and I have a hunch as to how he could afford a radio like this."

"You mean he stole it?" Chief Collig asked.

"We think he belongs to a ring of thieves," Frank told him. "If they fight among themselves, it would explain the trouble in Shantytown."

Lieutenant Daley looked doubtful. "If Sutton stole the radio, why would he plant it on Alf? That would only call the attention of the police to himself."

Frank grinned. "If you'd seen Sutton go after me, you'd know he acts first and thinks later."

"Then he's probably regretting Lundborg's arrest right now," Lieutenant Daley returned.

"That's not all he'll regret," Joe promised grimly, "if he's had anything to do with Chet and Biff's disappearance."

"That reminds me," the chief said. "The boys' parents received postcards from Northport, too. We're looking for the bald, loud-voiced man you told me about, but that isn't much to go on."

"No," Frank admitted, "but we're working on a new clue." He told of the discovery of the Fizzle soda bottle and the purchase of a similar one by the bald-headed man in Northport. "That's why we think he's connected with stealing the Sleuth as well as Chet and Biff's disappearance."

"Then," Joe put in, "we learned that the dock manager up there owns the Black Cat and rented it the day of the bank robbery to the bald fellow and Ben Stark-the one we saw talking to Hank Sutton in Shantytown."

Chief Collig looked at the boys keenly. "I see what you're driving at-that Sutton may be more than a petty thief-he and the other two might be involved in the robbery!"

As Lieutenant Daley stared at the Hardys in amazement, Frank replied, "You're right, Chief. But we have no solid evidence yet to back up our hunch. Joe and I will check stores in town tomorrow to see where the radio came from."

"Good. We'll do some checking of our own too. Thanks, Frank and Joe, for coming down."

When the Hardys reached home, their house was dark. They let themselves in quietly, went to bed, and fell asleep at once.

Some time later Joe was awakened by a noise. He sat up, listening. It came again-a soft knocking.

"Frank!" he whispered, shaking his brother. "Someone's at the front door."

Instantly Frank was awake. The boys hurried downstairs. As the gentle knocking began again, Frank switched on the porch light. Joe swung open the front door. Before them stood a tall, thin, worried-looking man.

"Mr. French!" cried Joe in surprise.

The costume dealer's mouth dropped open in astonishment. "You-you're not-you're here!" he stammered incoherently.

"Yes, of course, we are," Frank responded. "Why are you so surprised to see us?"

"Why-ah-I'm terribly sorry, boys!" Mr. French looked nervously over his shoulder. "I-I see I've come to the wrong street-looking for High Avenue, and this must be High Street. So sorry! Good night!"

The tall man hurried down the steps to a car at the curb and drove away.

Joe turned to his brother. "There isn't any High Avenue in Bayport. Mr. French must know that. He's been in business here for years."

As Frank closed the door, they heard footsteps at the top of the stairs and their mother's voice asked softly, "What is it, Gertrude?"

"Burglars!" hissed their aunt. "I heard them talking." She called down in a loud but shaky voice, "The police are coming! Go or I'll call my nephews! Frank! Joe!"

"We're down here, Auntie!" Frank informed her, stifling a laugh. "There are no burglars."

After a second's pause there came a weak "Well!" followed by "Humph! I might have known!"

"What's the matter, boys?" Mrs. Hardy asked.

"Someone here who said he had the wrong street," Joe told her, and switched off the porch light.

The next morning the boys ate an early breakfast. Afterward, Frank suggested, "Let's try all the appliance stores to see if Sutton did buy the Super-X radio. We can see Mr. French later."

Joe agreed and they set off. They went from shop to shop, but the story was always the same: The merchants did not stock the Yokohama Super-X radio-it was too costly to sell many sets. At last, however, a young clerk in a hi-fi equipment store said, "Yes, we have them. I'll be glad to show you one."

"We're not here to buy," Frank said. "We just want to know if you've sold any recently."

"No," the disappointed clerk admitted. "We don't sell many. We thought we would-despite the high price-because the Super-X transistor has so many extra features-FM, short wave-name it!"

"Where do you get them?" Joe asked.

"We import directly from the Yokohama Radio Company's distributors in j.a.pan. The radios come in by ship and are unloaded on the Bayport docks."

"Have you missed any from your stock lately?" Frank queried.

The clerk looked surprised, but answered readily, "No, but we were short one crate on the last shipment.

My boss wrote to the distributor in j.a.pan about it, but there hasn't been time for a reply yet."

The boys thanked the youth and returned to the street. They wondered about the clerk's remarks concerning the foreign-made radios.

"If Sutton bought the radio, he didn't buy it in Bayport," Joe declared.

Frank said, "He may have stolen the whole crate that was supposed to go to the hi-fi store. Let's cycle out to Shantytown. Maybe we can learn more about Sutton."

The brothers hurried home and put on their beachcomber clothes. Then they hopped onto their motorcycles and sped along Sh.o.r.e Road. They hid their cycles in a grove of short, scrubby pines near the squatter colony.

"We'd better walk the rest of the way," Joe said, "and act as casual as possible."

Frank and Joe entered the camp cautiously. It was noontime and pale smoke rose from a few cooking fires near the water. The village was nearly deserted and the boys judged that Sutton's shack was empty.

The door was padlocked.

As Frank and Joe wandered among the huts, they noticed that each one had a trash heap of its own in the rear. Suddenly Joe darted to a pile in which something glinted in the sunlight.

"What did you find?" Frank called, and ran forward to look.

"Pop bottles!" Joe exulted, holding one aloft. 'Fizzle soda!"

CHAPTER XII.

The Desolate Island JOE picked up another bottle from the rubbish heap. "It's exactly like the one we pieced together last night," he declared. "These prove the bank robbers are linked up with Shantytown!"

"It looks that way," Frank conceded. "But-Fizzle soda may be sold around Bayport. As you said, we don't know for certain that the robbers used the Sleuth. Somebody may just have 'borrowed' it for a joy ride."

"Well, the bottles make it likely that the robbers are connected to this place," Joe amended. "But let's scout around some more."

The two boys, hands in pockets, strolled casually among the shacks. Although they looked closely at the few squatters hanging around, they saw no one they recognized. Disappointed, the brothers circled back to the trash heap.