"Right. One of the thugs on the beach suspected it might have been an empty oxygen tank you boys had knocked over. But when they took the precaution of putting handkerchiefs over their faces, it gave me a chance to come along undetected by doing the same thing."

Leaving the thugs securely tied, Mr. Hardy led the boys toward the beach.

"It's my guess," said Frank, "they have the Dodds in one of those cars they're loading onto the barge."

"Then we'll have to stand them off until Collig's men arrive!" his father said.

He and the boys halted just inside the entrance and peered out through the curtain of rockweed.

The barge rocked gently at the tip of the dock, its lights out. A few cars were already aboard. The Hardys' own automobile stood nearby, while Birnham's truck was parked at the end of the gully. Guns and crates were being loaded into it quickly, as black storm clouds rolled ominously over the scene.

"Do you think the gang's lookouts may spot the police?" Frank murmured.

"Could be," his father whispered. "How many routes are there off this beach?"

"Just one-that gully over there," Chet answered. "It connects with the gra.s.sy slope to the top of the cliff."

A short time later the barge was fully loaded. A man began untying its mooring rope.

Mr. Hardy fastened his handkerchief over his face. "I'm going to draw some of them into the tunnel.

Think you boys can cause them a little trouble out there on the beach?"

"I'll handle the gully," Joe whispered.

"Chet and I will watch the barge," Frank offered.

When the boys had backed against the rock wall near the tunnel, the detective ran toward the barge and gave a m.u.f.fled shout.

"Hey, quick, some of you guys give me a hand with these kids in here!"

At once several footsteps pounded down the ramp onto the dock. Mr. Hardy dashed back into the tunnel. In a moment four men raced in after him. At once Frank, Joe, and Chet sprang into action.

Joe ran toward Birnham's truck, which was guarded by two men. After landing a stunning punch to one thief's jaw, he blocked the other with an upturned crate. Like lightning Joe leaped to the right-front tire and drove his pocketknife deep into the thick rubber until it collapsed. Yanking out the knife, Joe bounded into the gully.

Meanwhile, Frank and Chet were sprinting to the barge ramp. As Frank glanced back, he saw Chet trip, and the stocky figure of Birnham rushing to tackle him. Chet threw him off, however, and Frank rushed onto the ramp. Two men on the barge charged him.

Sidestepping the larger thug, Frank recognized the second man as Montrose. The boatman raised a tire iron, but got no further as Frank's head rammed into his midriff. With a groan, Montrose toppled backward onto the dock.

The next second Frank felt a sharp blow on his shoulder and the two strong arms of Slagel dragged him out to the beach. Slagel thrashed at Frank with his cane and the two rolled over and over in the wet sand.

Suddenly the sound of wailing sirens put an end to the struggle. Slagel leaped up and bolted toward the tunnel. At the same time came a shout. "Cops!"

Dazed, Frank staggered to his feet in time to see four men climb into the brothers' car and race it into the gully!

Searchlights flashed on the beach and policemen swarmed down the gra.s.s slope. Just then a figure darted past Frank onto the barge. Melliman! Before Frank was halfway up the ramp, Melliman had kicked out the tire braces of one of the cars and rolled the car over the edge into the water.

For an instant Frank wondered why. Then he thought, "The Dodds must be inside!"

Melliman now leaped aboard the adjacent fishing boat. By this time Frank was in the water swimming in the direction of the sinking vehicle. When he reached it, Frank could see the three helpless Dodds within.

The water was rising rapidly. Frank pulled on a door, but the pressure against it was too great!

"Hold on!" he yelled.

Fortunately, two policemen had followed Frank. Together, they pulled the door open, yanked the Dodds out, and bore them safely through the rising waves to the beach.

Chief Collig rushed up. "Are you all okay?"

"Fine, thanks, sir," Jack gasped as he was cut loose. His father and uncle, having swallowed some water, coughed violently but soon were able to stand up.

"The crooks escaped in our car!" Frank exclaimed, starting toward the gully.

Collig stopped him. "Your brother pulled a fast one on them. He waited at the top of the cliff until they were halfway up the slope, then unfastened the netting. As it slid down, they couldn't move, and our men caught them. Your dad, after tunneling up half the gang, also took care of this fellow with the cane. He was still out cold when we handcuffed him!"

Just then Joe ran up, his face flushed with excitement and relief at the Dodds' rescue. When Mr. Hardy joined the group, the others learned that Melliman had not escaped in the fishing boat. "Apparently he couldn't get it started."

"And why not?" asked a familiar voice with a proud ring in it.

"Chet!"

Soaked to the skin, Chet added, "A knowledge of botany goes a long way-especially in learning to knot seaweed into a boat propeller!"

By now, Slagel, Melliman, and the rest of the prisoners had been led away to police cars on the cliff above. Only Collig and another officer remained on the beach with the Hardys and Dodds. The tide was rolling in now, and jagged streaks of lightning could be seen.

"How can we ever thank you Hardys and Chet enough!" Mr. Dodd said.

Collig added, "You boys will be receiving a handsome reward for your work."

Joe's eyes glistened. "I think there's another case we're going to solve tonight-the Pilgrim mystery." He sloshed through the surf which had almost covered the beach. Chet, Frank, and the Dodds joined Joe as he pointed to some leaves along the cliff. Puzzled, Mr. Hardy and Collig watched from the remaining strip of dry sand.

"I noticed this algae earlier tonight, and if I'm not wrong, it matches the leaf in the Pilgrim message," Joe declared.

"You're right!" Jack exclaimed. "But the message seems to indicate a place on land."

"Maybe we've been on the wrong track," said Frank. "Professor Dodd, can you remember the last words of the clue?"

The tall professor knew them by heart." 'Crash of countless breaking black-'"

" 'Billows'! Not willows!" Joe finished. "Waves would break in a hurricane as well as trees."

"Joe!" the professor cried excitedly. "My calculations on the position of Venus-which is now obscured by clouds-had led me to this area of the coast a short time before I was seized by Slagel's men!"

Chet pulled a soaked book from his pocket. "That growth is chondrus crispus-Irish moss."

Frank exclaimed, "It was several hundred years ago when the Pilgrim family perished! Since that time, this coastline may have fallen several feet and water may now cover the location of their shelter."

"Then there may be a cave in the slope near where we're standing!" Jack cried out.

Another streak of lightning could be seen in the distance and the waves were rising over the moss-covered rock.

"Let's look before the storm gets here!" Joe urged.

With flashlights turned on the scene by the men, the four boys kicked off their shoes, stripped to their shorts, and dived in. Suddenly Frank came up and shouted, "I see something!"

Chet, Jack, and Joe swam over to him. Then all four vanished beneath a rough wave. Twenty seconds later they surfaced, holding a heavy object. Treading water, they maneuvered the object to the beach.

It was a steel-bound wooden chest!

Excitedly they set it down in the sand beyond the incoming tide, as the rest of the group rushed up. The metal had rusted almost to powder, and several holes gaped through the rotting wood. With Joe's help, Jack raised the wobbly lid, and everyone stared in wonderment.

Piles of green and blue jewels, strings of ruby beads, and rotted pouches of gold coins glistened with sea water amid brown weeds and Irish moss. Near one corner lay a large, algae-covered object.

"Look!" Martin Dodd exclaimed excitedly.

It was a bottle! He handed it to Jack's father, who carefully unstoppered it and removed a long roll of worn papers. The others gathered around as he read the first words aloud: " 'The Record of a Perilouf Voyage in Fearch of the Horfefhoe-Fhaped Inlet, in the Year of Our Lord 1647, by Eliaf Dodd.'"

"We've found it!" Jack exclaimed.

As a streak of lightning creased the black skies, Frank glanced up at the cliffs. Suddenly he cried out, "There's the answer to the clue's last words!"

At the next flash the others looked up at the glistening rock. It had all the appearance of a vein of gold!

Drenched but happy, everyone walked toward the brothers' car. Each of the four boys bore a corner of the chest. Frank and Joe wondered if any case as exciting as the one just solved would ever come their way. They were soon to find out, when challenged by The Secret of the Caves.

Frank now smiled at the Dodds. "How about a lift?"

"Only if you'll promise to share Thanksgiving with us this fall," Jack answered. "We're going to have a feast that would make our ancestors proud! And you're going to join us too, Chet. We'll even have a special seaweed menu for you!"

"No roast turkey and sweet potatoes and-" Joe asked.

"Or chocolate cake with frosting," Frank added.

Chet groaned. "Stop it! Anything but seaweed!"