Before Joe could say more, Frank was overboard and swimming toward the ghostly lights. He was midway between the two crafts when Joe saw the black fishing boat. Joe stiffened with fear as he deciphered the international code message which was being flashed by lights from the fishing boat to the barge.

"O-n-e o-f H-a-r-d-y k-i-d-s s-w-i-m-m-i-n-g t-o-w-a-r-d y-o-u. S-t-o-p h-i-m."

Joe jumped into the water instantly and swam toward his brother. Frank, fighting strong currents, had not noticed the warning. Minutes later, he reached the barge and caught his breath. Then, grasping the damp wood with his wet hands, he pulled himself up and slid noiselessly over the side next to a braced car.

Suddenly someone struck him a hard blow on the head. His next sensation was of falling to the water.

Frank blacked out before he reached it, but revived as he felt two arms grab him and take him to the surface.

Desperately, Joe bore his brother through the waves to the darkened Sleuth as the noise of the barge motors became fainter and fainter.

Joe was almost at the end of his strength when he touched the hull of the Sleuth. Chet leaned over and hauled Frank, semiconscious, aboard.

The next instant, Joe heard Chet cry out and saw him topple backward out of sight.

Grabbing the rail, Joe swung into the stern of the boat. To his horror, Chet lay motionless beside Frank.

Joe whirled to face the attacker-a muscular, black figure in a glistening skin-diving suit.

The man raised a sharp, dripping piton and lunged at Joe!

CHAPTER XVI.

Retreat Trick BLOCKING the thrust of the spike, Joe threw all his remaining strength into a hard-fisted uppercut. The blow sent the diver reeling against the fan-tail of the Sleuth. Staggering, the black figure noticed Chet beginning to revive. In a flash he dived overboard and disappeared.

Joe hurried over to Frank, who by now was sitting up groggily. "Thank goodness you're all right," he said. "Chet, you okay?"

Chet winced and rubbed his jaw, but smiled gamely. "You Hardys are the ones I'm worried about!"

"You can't keep us down!" Joe said with a grin as he helped Frank to his feet.

"Thanks for saving my wet skin," Frank said.

Shivering, Joe crouched out of the wind and started the engine. He pointed to starboard. "Look!"

Fifty yards away the fishing boat idled in the waves, its lights extinguished. Through the darkness, the boy could see its pilot pulling another figure aboard. Then the boat sped in the direction of Bayport.

"Let's go!" Frank said.

The Sleuth followed. It was just closing the gap near the mouth of Barmet Bay when the motor began sputtering. The gas gauge read empty. In disgust the boys watched the black boat vanish down the coast.

"How are we going to make the boathouse?" Chet asked nervously.

Frank pointed to the emergency oars. "The tide's coming in, so that'll help us row."

Joe was angry about the fishing boat and its occupants getting away. Frank consoled him. "At least we've learned the owner of that boat is in on this racket. Also, I'm sure we had our first meeting with the spider-man!"

"Who?" chorused Joe and Chet.

"The skin diver-he's powerful enough to scale cliffs. And that pike he had is used for mountain climbing."

Chet shuddered. "Or a weapon."

"He's the one who trapped Callie in the net," Joe added.

Frank expressed disappointment at his failure to get a look aboard the barge or at the man who had knocked him into the water. "We'll have to tackle the problem from another angle."

"Not tonight!" Chet begged. "We've had enough."

The Hardys agreed and the boys rowed wearily to the boathouse.

First thing the next morning Frank checked with police headquarters. There were no leads to any of the missing Dodds. The brothers were discussing what move they should make next, when the telephone rang. It was Tony Prito. He excitedly asked the boys to come to the Napoli's boathouse at once. "It's important!"

When they met him, Joe asked, "What's up?"

"Can't tell you yet." Their friend, wearing swimming trunks, hurried them aboard his motorboat and steered north out of Barmet Bay. He slowed down just past Bay Bluff.

"I think I saw something out here yesterday, and if it's what I suspect-"

Tony headed toward the sh.o.r.eline, studying the water closely. Suddenly he cut the motor and leaned over the side. The Hardys followed his pointing finger.

"Down there!"

Beneath the gray surface of the water, a slight glimmer of light was visible. Straining their eyes, Frank and Joe could make out part of a green-and-white object. Their hearts jumped.

"Jack's boat!" Frank exclaimed. "Do you think-" He did not voice the dreadful thought that crossed each boy's mind.

Tony said tersely. "We won't know until one of us goes down there. I'll go!"

Tensely Frank and Joe watched Tony's lithe body cut the water and his distorted image vanish into the depths. They waited in grim silence.

When Tony's head broke the surface, the look on his face brought vast relief to the Hardys. "It's the Dodds' boat all right, but n.o.body's in it." He climbed aboard the Napoli. "Do you think their kidnappers scuttled it?"

"Probably," Frank guessed, "they wanted the boat out of the way so that the police would think the Dodds had escaped in it. We'd better report this right away."

Tony drove back to Bayport and the brothers went home. They had just entered the kitchen, door when the telephone rang. Joe answered it.

"Joe Hardy speaking."

The voice at the other end said crisply: "Kid, you and your brother have meddled enough. If you ever want to see your friends alive again, get out of town and stay out for five days-it might be good for your mother's and aunt's health too. This is your last warning! And be sure to take a look out your front window before leaving"

When Joe heard the receiver click, he hung up and told Frank of the threat. "It was Slagel, I'm sure."

The brothers ran to the front windows.

Between two trees along their quiet street, a black sedan was parked. Two strangers sat silently in the front seat watching the Hardy house.

Joe was upset. "We can't just obey Slagel-but we can't ignore a threat to Mother and Aunt Gertrude, either. What choice have we? Maybe we should call the police."

Frank thought a minute, then his eyes lighted up. "Not yet, Joe. Let's try our wooden-horse operation!"

The boys suddenly realized how well their secret plan would work during the present predicament. Joe led the way upstairs. "Of course! If we leave now for Harpertown, we could buy the car while we're 'vacationing.' And then-" he grinned-"gallop into Troy!"

The boys brought down suitcases from the attic and packed them hastily. While Frank changed into Bermuda shorts and a light jacket, Joe opened a closet and brought out a fishing rod, surfboard, and an air mattress. "We may as well make it look good."

Frank was sober. "We'll have to let Mother and Aunt Gertrude know why we're leaving, but I hate to worry them."

"We'll have to tell them for their own safety. Besides, it's the best reason we've had for a vacation in a long while!"

Twenty minutes later, their bags and gear at the foot of the stairs, the brothers went into the kitchen and told the two women of the threat. "But we'll be able to return to Bayport in less than a week," Joe added.

"We'll phone you as often as we can," Frank a.s.sured them. "It will be the only way for us to know you're both safe."

Mrs. Hardy's pretty face showed worry, but she forced a smile and kissed them. "Frank-Joe-take care of yourselves. You promise you'll be able to return in a few days?"

"We may be home sooner than you think." Joe chuckled.

Aunt Gertrude's face wore an expression of militance. Removing her ap.r.o.n, she took a large frying pan off a hook.

"Just where are these two men watching our house?" she asked, brandishing her weapon. "Who do they think they are, threatening my nephews I"

It took Laura Hardy's help to restrain their courageous relative from marching outside. Finally she replaced the frying pan.

"Aunty," said Frank, "this isn't really a Hardy retreat. It's sort of a strategic withdrawal."

The boys made two quick telephone calls, one to Chet, and the other to telegraph their father. Then they took some cash which they kept in the house safe. Picking up a suitcase, Frank turned to Miss Hardy.

"Aunty, you and Mother can help by showing a lot of emotion out at the car. We want to impress those men."

The two women did their part. When the boys had loaded all their luggage and vacation equipment into their father's car, Mrs. Hardy embraced them fervently. Aunt Gertrude's eyes were red as from weeping.

In each hand she held a concealed onion. From their car, the two men watched the well-staged scene.

Amidst much waving Frank and Joe pulled down the driveway and drove up the street. The black sedan moved out and followed.

When the boys reached the highway beyond the city limits, Joe glanced back at the car following. "Next stop Harpertown," he said. "Then the wooden horse!"

CHAPTER XVII.

The Wooden Horse FRANK kept the car at a leisurely speed. In the rear-view mirror he and Joe could see the black sedan fifty yards behind them.

"If we go any faster," said Frank, "those men will think we're trying to shake them. I want them to keep thinking we're just going on a vacation."

Using Route 10 and then the State Highway, the Hardys rolled along toward their destination. They had ten miles to go when Joe murmured, "They're still trailing us."

In Harpertown the Hardys headed for the beach resort area. Soon they drew up before a large seaside motel.

Frank took several bills out of his wallet and handed them to Joe. "We'd better pay for a week to make it look good."

Frank stayed behind the wheel while Joe went in to register. When he came out again, they took their luggage from the trunk.

"Our friends are still along," Frank whispered.

Joe could see the black sedan parked to their rear half a block away. Paying no attention, the boys carried their gear in two trips up to their second-floor room. On the last trip, Joe overheard the sedan's driver checking the Hardys' length of stay with the desk clerk.

In the room the boys changed into swimming trunks. "It's a shame we can't enjoy what we paid for "

Frank smiled. "But we'll put on a good act for our two friends."

When the Hardys returned from a brief swim, the black car was gone. "Think we've convinced them?"

Joe asked.

"Yes. They're probably hightailing it back to Bayport to attend to their-er-business."

It was early afternoon when the brothers walked to a used-car lot in the Harpertown business district-the one Frank had scouted on his previous visit.

They looked over several late-model cars. Joe smiled. "It doesn't seem possible we're actually going to own a car."

"You're right."

The heavy, round-faced owner approached them. His manner was friendly and he talked volubly.

"Thought I remembered one of you fellows," he said, walking around with them. "What kind of car are you looking for?"

"Something pretty flashy, if it's not too expensive," Frank said.

"At least a year old," Joe added, recalling the points common to the cars stolen on Sh.o.r.e Road. "And nothing foreign."

The man knit his brows, then pointed out several large cars. He came to the end of a row. "Here's a nice Booster six-cylinder job, white walls, power steering-"

The boys regarded the two-tone brown sedan, then shook their heads. "None of these are as sharp-looking as we wanted. Have you anything else?"

The owner led them to a far corner of the lot. He pointed to a handsome, sea-green Chancellor, a model two years old. Excited, both boys walked around it several times.

"She's a real limousine all right," the dealer acknowledged. "But her engine's not the best and the carburetor could use some work. Wouldn't buy her myself, but if you boys want a flashy car, that's the one."