"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 Japan!"

  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."

  "Sutton had a Yokohama radio!" Joe exclaimed. "And we saw him talking to Ben Stark that day at Shantytown."

  "The radio seems to be a connection between them," Frank pointed out. "I think we'd better go back to the hi-fi shop, and find out more about the identity of Yokohama Super-X purchasers."

  After eating breakfast, the boys hurried off, first to pick up their motorcycles, then to go to the hi-fi shop.

  When they entered the store, the young clerk was glad to see them.

  "Change your minds, fellows?" he asked hopefully. "Like to buy one of those sets?"

  "We would like to look at them," Frank replied.

  Immediately the clerk bustled off and returned with four of the compact little radios. "Go ahead," he invited. "Try them."

  While Joe flicked the button on one set, the young man said, "These are neat. As I told you the other day, we buy them from a distributor in Japan." In response to Frank's query about who had purchased them, the clerk gave the customers' names, all familiar to the Hardys. None of

  them could be suspect.

  "Three of these radios came in yesterday afternoon. I could give you boys a good price, since we bought them at a big discount."

  "How come?" Frank asked.

  "Well, we didn't buy these from the distributor," the clerk admitted. "These were brought in by a fellow who wanted to sell them at a secondhand price, even though they're brand new. My

  boss snapped up all three. He knows a bargain."

  "I see." Frank nodded. "No questions asked."

  "Oh, it's not anything illegal," the clerk hastened to say. "They were brought in by a respectable businessman, Mr. French, who owns the costume store down the street."

  "Mr. French!" the boys echoed in amazement.

  "Yes. What's so strange about that?"

  "Oh, nothing, I guess," Frank replied. "You just reminded us that we must see Mr. French ourselves right away. The radios will have to wait. Come on, Joe!"

  While the mystified clerk stared after the Hardys, they bolted from the shop and hurried along the sidewalk toward the costume shop.

  "Mr. French again," Joe muttered, shaking his head. "Is he one of this gang?"

  "Somehow I trust him," Frank replied. "Maybe the robbers are forcing him to play along with them, and have threatened harm to his family unless he does."

  "He didn't look very happy the afternoon we picked up our costumes," Joe recalled. "Those men in his shop were threatening him. And when he came to our house in the middle of the

  night, it was no mistake!"

  "He knows Dad's a detective," Frank said. "I think he wanted him and was confused when we answered the door."

  "Well, we'll soon find out," Joe said as they neared the shop.

  "It looks closed," Frank remarked. The heavy door was shut and the blinds drawn. Going closer, the boys saw a sign in the window: CLOSED INDEFINITELY

  "I wonder why," said Joe. "Has Mr. French gone out of business?"

  "Hey," Frank cried out, "where are the gorilla and magician outfits that were in the window yesterday afternoon?"

  Only one costume was now on display-a skeleton suit, which stood up with outspread arms, like

  a scarecrow!

  "I hate to think what that costume means, if it's a signal," Joe said.

  "Never mind," Frank said. "We must find Mr. French. Perhaps he lives over the store." Frank strode to a door at one side of the building. "Yes, here's his name on the bell plate."

  Impatiently the young detective jabbed with his thumb at the button. The bell sounded loudly

  but no one answered.

  "Hey!" came a sharp voice. "What are you two doing here?"

  Frank and Joe whirled to face their two chums Jerry Gilroy and Tony Prito.

  "We're sleuthing around," Joe replied, and grinned. "What are you fellows up to?"

  Tony explained that he and Jerry were on an errand for Mr. Prito, then asked, "Have you found out anything more about Chet and Biff?"

  "We found out plenty!" Joe exploded. "Chet and Biff were kidnaped by the bank robbers, who mistook them for Frank and me."

  "What!" cried Tony and Jerry. While they listened intently, Frank and Joe gave the details of their adventure the night before.

  "But where is the gang holding them?" Jerry wondered. "Could it be Hermit Island?"

  "Could be," Frank said. "We found out the hermit we saw is a fake. The real one's dead."

  "And when Dad trailed Stark and Moran last night," Joe put in, "they went to the dock and waited for a boat. That could mean the rest of the gang-and Chet and Biff-are some place only

  accessible by water."

  "Then what are we waiting for?" urged Jerry. "Let's head for Hermit Island!"

  "Yes-and no girls this time," Tony added. "That phony hermit carries a shotgun, and if the robbers are there, the danger is double."

  "Right," Frank said. "We'd better take both boats, Tony. In case of trouble, we'll be able to split up, or help each other."

  Tony agreed eagerly. "Then we'll meet you at your dock at one-thirty," Frank told him.

  As their two friends hurried off, Frank and Joe walked to their motorcycles and rode home.

  As they dismounted in front of their garage, Aunt Gertrude appeared behind the back screen

  door, wringing her hands nervously.

  "Hi, Auntie!" Joe called cheerfully. "Where are Mother and Dad?"

  "Your mother has gone shopping and your father's off on some more detective work! There's a giant in the living room waiting for you."

  "A what?" Joe asked, entering the house.

  Aunt Gertrude made a sweeping motion with her arms. "A man," she said, "a great big man!"

  Laughing, Frank led the way into the living room. This must be Alf Lundborg!

  The visitor's huge frame certainly dwarfed the Hardys' furniture. Grinning, he shook each

  brother's hand in his crushing grip.

  "I'm out of jail again," he told them. "Sutton wouldn't say I attacked him, so they finally let me go."

  "I knew you didn't do it, Alf," said Joe.

  The stevedore's good-natured face clouded. "No, I wouldn't touch a little weasel like Sutton,"

  he agreed.

  "But it makes me sore to be accused of doing it! What I came to tell you, though, is this-I know who did beat him up. It was one of his own pals!"

  "Ben Stark?" Frank asked curiously.

  "No, a fellow they call Pops. Remember I told you about the bunch who were always fighting with one another? Well, Sutton and Pops do most of it. Pops finally gave it to him good, but

  Sutton won't tell the police."

  "That must mean they're in something illegal together," Frank reasoned. "How about this Pops, Alf-is he an old man?"

  "No. Although he's bald, he's younger than Sutton-bigger and stronger. Talks loud, too. I don't know why they call him Pops."

  Frank and Joe looked at each other excitedly Both immediately thought of Ben Stark's pal who

  was still at large. Could Pops be the Fizzle soda drinker?

  "Thanks for telling us, Alf," said Joe. "We're glad you're out of jail. You've been in twice and both times because of us."

  "You couldn't help it," replied their big friend, "and you spoke up for me both times. I appreciate that."

  After Alf had left, the brothers had some lunch, then headed for the waterfront on their

  motorcycles.

  Tony and Jerry were already in the Napoli when the Sleuth came alongside the Prito dock. With

  serious, determined faces the four friends headed for Hermit Island.

  As soon as they reached the ocean, the boys were confronted by a fast-darkening sky and

  choppy sea.

  With incredible swiftness, black clouds, with chains of lightning snapping underneath them,

  moved in from the south. Large raindrops began to pelt the boys. In another moment the

  darkness closed around them like nightfall. Lightning flashed on the heaving ocean and the rain smacked down on them almost painfully.

  "Why didn't we bring slickers!" Joe exclaimed.

  Through it all, Joe kept the Sleuth's nose pointed northward. Presently, illuminated by the

  lightning, a rocky mass came into view.

  "There's the island," Frank called out. "A motorboat's just pulling away, Joe!"

  "Let's chase it!" Joe cried. "Some of the gang may be aboard and are escaping."

  "Not now," Frank cautioned. "Chet and Biff come first!" As the boys watched, the dark-brown craft disappeared in the distance.

  As suddenly as it had come up, the black squall passed over. The Sleuth and the Napoli circled toward the island's beach. By this time the rain had stopped.

  The clouds parted, blue sky appeared, and the sun beat down again. Under its burning heat the

  boys'

  clothes began to dry out.

  "The storm's probably driven that phony hermit under cover," Joe said. "Let's get ashore before he spots us."

  The boys found a small cove fringed with small, scrubby oak trees. Quickly concealing their

  boats in this cover, they debarked and set out on the path around the island.

  This time no one disturbed them. The trail climbed and then dropped down to the level of the

  shore again. Overhead loomed the wet bluff.

  Suddenly Frank stopped and pointed to a dark opening in the gray rock ahead. "A cave!" he said quietly.

  The boys crept nearer. Just outside the cave's entrance, Frank lifted a warning hand.

  "Voices!" he whispered.

  CHAPTER XVII

  Hermit's Hideout

  HOLDING themselves rigid against the damp rock, the four boys strained to listen. Somewhere

  inside the cave a man was talking rapidly, but his words were muffled and indistinct.

  "What's he saying?" whispered Tony.

  Frank motioned for the others to hold their places. Then he lay on his stomach and inched

  cautiously forward until his head was just outside the cave opening. From this position he could hear what was going on inside.

  "Well, what's happening?" Jerry whispered impatiently. "Tug at his ankle, Joe!"

  But just then Frank came wriggling backward. He jumped to his feet, and clutching his sides,

  hastened some distance down the path.

  Joe, Tony, and Jerry ran after him.

  "Frank-what's the matter?" his brother asked. "What was he saying?"

  Frank tried to speak, but his chest heaved with suppressed laughter. Finally he managed to tell them: "The fellow was saying . . . 'B-buy B-b-butterfly Baby Foods'!"

  "Wha-a-t!" The three boys looked at one another, completely mystified.

  "We were listening to a radio," Frank blurted out. "The announcer was giving a commercial!"

  "You mean the hermit's in there, listening to the radio?" Joe asked.

  "I couldn't see," Frank replied. "Maybe Chet and Biff are there! It's likely, anyhow, that their guard went in to avoid the rain. Now that it's over, he'll probably come out again. Our best

  move is to find a good spot to lie in wait for him."

  Near the cave mouth the boys found a large, brush-protected boulder and hid themselves

  behind it. For some time they waited. From inside the cave, snatches of music alternated with

  the announcer's voice.

  At last Joe could stand it no longer. "Maybe there's nobody inside!" he burst out impatiently.

  "I'm going to have a look!"

  "Careful!" Frank whispered, as his brother slipped out of hiding.

  Joe darted to the path, lay down, and inched himself forward until he could see into the cavern.

  For several minutes he peered inside, then scrambled back behind the boulder.

  "Somebody is in there!" he reported. "He's asleep and forgot to turn off his radio."

  "Any sign of Chet and Biff?" Frank asked.

  Joe shook his head. "No."

  "Do you think it's the hermit?" Jerry asked.

  "I don't know," Joe replied. "Anyway, he's alone."

  "We could surprise this fellow while he's asleep," Tony said.

  Frank nodded. "But Chet and Biff may be somewhere else on the island. Let's search while the fellow in the cave is asleep."

  "Good idea," Joe agreed. "Look for a hut or shelter where the boys might be prisoners."

  A brief examination of the gray bluff revealed a narrow cleft leading to the top of the precipice.

  Joe, ascending first, found himself on another path which seemed to rim the island from the

  top of the bluffs.

  "Here's the trail the hermit used to keep us in sight yesterday," he told the others.

  After scrambling up, Frank, Tony, and Jerry paused for a look about. Below them sparkled the

  bright ocean, extending to the mainland a few miles away. Behind lay a little plateau,

  overgrown with small pines and scrub oaks. In the center of the flat area rose a steep, rocky hill which gave the island its humping silhouette

  "A hut would be easy to camouflage among those trees," Frank remarked. "We'll have to spread out and comb every foot of the woods."

  Though the youths worked carefully around the plateau, they found no sign of any shelter. On

  the island's

  seaward side, where the growth was sparse, the boys checked the sides of the steep hill for

  caves. They saw none.

  "It doesn't look very hopeful," Joe said at last. "If Biff and Chet were brought here, they've probably been carried off by now."

  "The robbers might still be using this place," Jerry insisted. "It's a perfect hideout."

  "They could have come here with the loot from the bank," Tony added, "and used the phony hermit to scare off intruders."

  "Perhaps the gang is using the island merely as a stopping-off place," Frank suggested. "With this hill right in the middle, a lookout could spot boats approaching from miles away."

  "Of course!" Joe took him up eagerly. "That's how the hermit happened to be waiting for us yesterday.

  Today is different. Don't forget that boat we saw pulling away. Chet and Biff may have been put aboard!"

  "Right," said Joe. "Let's climb to the top of the hill and determine how far we can see."

  Sparked by the new idea, the four boys attacked the steep hill at the center of the island. They worked their way among the rocks and pulled themselves upward by means of the short, tough

  brush.

  "What a rough climb!" Jerry gasped.

  As they climbed higher, the vegetation became too flimsy to use as support, and the hill's cone became even steeper. Still the boys pressed upward, panting, with Frank in the lead. Finally he clambered onto a flat, wind-swept area at the top-about twenty feet across-and threw himself

  down to rest.

  Joe's head popped into view over the edge, and then Jerry's. Suddenly, from below them, came

  a sharp cry.

  "Tony!" yelled Joe and Jerry together.

  Sitting up, Frank saw a cloud of dust and stones tumbling and bouncing down the hill. A whole

  section of ground slid like a carpet along the steep slope, with Tony in the middle of it!

  Frank, Joe, and Jerry slid in pursuit, bracing their feet hard against the slope like skiers!

  Partly covered by loose earth, Tony Prito lay on his back where the hillside leveled off. He

  grinned up weakly at his three chums.

  "You okay, Tony?" Joe cried anxiously.

  "Think so. Can't seem to get up, though."

  "Where are you hurt?" Frank asked.

  "Ankle," Tony answered, rising to one knee.

  Immediately a wince of pain crossed his face and he sank back again. Quickly Frank and Joe

  lifted their comrade to a standing position.

  "Try now, Tony," Jerry urged. "Put just a little weight on it."

  Though Tony's left leg appeared sturdy enough, the right one buckled at any pressure.

  "It might be a fracture," Frank said. "We'll get you to a doctor, Tony."

  While Jerry steadied the injured boy, Frank and Joe made a chair for him by interlocking their hands.

  Then they lifted Tony, who braced himself with one arm across each brother's shoulder.

  Slowly the little procession made its way down to the level of the plateau. Moving more rapidly now, they followed the path around to the mainland side of the island.

  Once among the scrub oaks and pines, the trail became too narrow for three persons to move

  abreast.

  Frank and Joe had to kick their way through the brush on each side as they advanced.

  When they neared the beach at last, a small pine clump hindered Frank's progress. He kicked

  out determinedly.

  "Hey, what's that?" cried Tony from his perch.

  A dark garment, struck by Frank's foot, flopped into the path!