Swim fins, also of Italian make, were lying on a table. They were the shoe type, put on like a pair of slippers. Rick identified an underwater camera, complete with steering fins and outside controls, and a number of face masks with built-in snorkels. Boxes stacked on the floor carried labels that identified them as midseason suits of French make.

"We've found some real fancy frogmen," Scotty observed. "This place looks like a high-priced show-room for diving gear."

"Pretty plush," Rick agreed.

They wandered back down to the beach and found that this area of the island was apparently more open to the sea. There were bits of flotsam, including coconuts that had washed in. The sea sh.e.l.ls were larger, and they found a few worth picking up.

Scotty beckoned and pointed to a piece of wood, nearly buried in the sand. "What do you make of this?"

Rick examined it. It was curved, and a shred of green metal still clung to the rusty remains of an ancient hand-fashioned nail. He looked up with sudden excitement. "It's a section of a ship rib. And a pretty old one, too." His finger indicated the shred of metal. "Copper. Or used to be." He broke it off. "Completely oxidized. It's been in the water a long time, perhaps even centuries."

The boys stared out at the reef, both half afraid to put their thoughts into words. Finally Scotty asked, "Do you remember reading about any earthquakes or big tidal waves down here recently?"

Rick tried to recall. "No. Why?"

"Well, the _Maiden Hand_ has been under the water out here for a couple of centuries--and in pretty deep water, too. It would take some disturbance that could reach down a hundred and twenty feet to break off a chunk."

Rick grinned. "You're right. But we haven't anything to lose by taking a look, have we?"

They trotted down the beach toward their own house at a half run. Rick looked at his watch. "At least one pair of tanks should be full by now, and there's plenty of time for a dive. Come on!"

They paused at the pier, put the pressure gauge on the first two tanks in series, and found them charged, as Rick had predicted. Then they ran for the house.

Zircon and Tony were gone and there was a note on the living-room table.

"_We're exploring the southern end. Be back in an hour or two._"

"Shall we wait?" Scotty asked.

"No need. We can take our floats. Let's get going."

They changed to trunks. Then, since they would not have anyone on the surface to keep track of time or depth, strapped on wrist watches, compa.s.ses, and wrist depth gauges. Floats and weight belts were put on, then the boys added small plastic slates and pencils for writing underwater. Knives, masks, snorkels, their favorite guns, fins, and lungs completed their equipment.

"Shall we walk up the beach, or swim?"

"Swim," Rick said promptly. "This stuff is too heavy to carry comfortably."

They launched floats, placed aqualung mouthpieces on top of their masks, and swam parallel to the beach. By using snorkels they avoided the effort of lifting their faces out of water to breathe and conserved the air in the tanks. With effective but effortless leg strokes they moved along rapidly.

As they approached the ship rib that Scotty had found they turned and swam straight out toward the reef, crossed it, then came to a halt.

"Let's tie our floats to something," Rick suggested, and Scotty nodded.

Aqualung mouthpieces replaced the snorkels, and each boy tested his flow of air, checked to be sure his mask was connected to the lung by a safety line, charged his gun, and set his watch. The watches, designed especially for underwater swimming, had an outer dial that could be set to show elapsed diving time.

Rick hooted and pointed down. Scotty nodded and they submerged. Because of their belt weights, and the weight of air in their tanks, they were just heavy enough to sink slowly. After the dive, when the air in the tanks was nearly exhausted, they would weigh about five pounds less and have a slight positive buoyancy that would help them to rise.

They found coral outcroppings and tied their float lines, being careful not to cut their hands. Rick suddenly wished they had brought canvas gloves. Scotty still wore a single rubber one.

Then, with a few strong kicks to overcome their inertia, they started down the face of the reef. It fell off sharply for about forty feet, then more gradually until sand bottom was reached at about ninety feet.

Rick felt the sensation of thrusting his face into a wedge as the pressure increased. He swallowed a couple of times and felt his ears equalize, but his mask was beginning to hurt. He exhaled through his nose and equalized the pressure inside the mask.

There were plenty of fish around now. A grouper saw them coming and ducked into his hole in the coral. A fairly large moray eel, only his head visible, watched their progress. Tiny demoiselles fluttered around them, and a pair of red squirrelfish watched from the shelter of a purple coral fan.

The coral growth was spectacular, with fantastic shapes and colors.

Then, as they went deeper, the colors gradually faded to a uniform green. Rick knew from underwater flash photographs that the appearance was deceptive. The colors remained, but the quality of light changed.

Scotty hooted four times, the signal for danger! Rick looked and saw a barracuda hovering near by. He gulped. The fish was easily five feet long. Both boys lifted their spear guns just in case the 'cuda attacked, but the motion alarmed him and he was gone with one powerful flick of his tail.

Rick consulted his wrist depth gauge, holding it close to his face plate. They were at bottom at ninety feet, and the clean sand dropped away at an angle of about thirty degrees. The boys planed downward, a few feet above the sand until Rick's gauge read 120 feet. This was the limit of their dive. Going deeper would mean stopping for decompression on the way up.

He recalled that the waves came into the beach from a slightly northerly direction and motioned to Scotty that they should turn north. Scotty moved out to the limit of visibility, and they swam on a compa.s.s heading of north, watching for any sign of a wreck. Now and then a coral shelf extended out from the reef, but they saw nothing that could have been a wreck. Once they swam over a patch of marine growth perhaps twenty feet long and ten wide, and a huge eagle ray lifted from it and glided off like a weird futuristic airplane.

It was quiet, except for the regular chuckle of their exhausts, and the light was subdued and even. It was a world without shadows. Still, Rick thought, there was plenty of light for photography. Next time he would bring his camera.

The watch showed him that over half their allotted time was gone, and he hooted once to Scotty, then reversed course, heading back toward their floats.

They approached the patch where they had seen the ray and Rick paused suddenly. There was an odd shape on the sand near the patch. He flippered over to it and examined it. Scotty joined him. It looked like an oversized mushroom protruding from the sand at an angle.

Rick unsheathed his knife and poked at it. The sharp tip penetrated for a fraction of an inch, then stopped. It was either rock or metal, and judging from the shape, it was unlikely that it was rock. He put his knife under it and pried, and the thing moved in the sand.

Both boys went to work on it, scooping the sand from around it. In a moment they had it clear. It was something like a dumbbell, covered with marine growth where it had been above the sand, but fairly smooth under it.

Rick took his belt slate and scribbled, "Metal."

Scotty nodded. Then both of them turned to look at the patch of marine life.

A distant throb, as though of a boat, caught their attention. They looked up, but the surface was invisible.

It was Tony and Zircon, Rick decided. They probably had returned to the cottage and found the diving equipment missing. They could spot the location where the boys were diving easily enough, first by the floats, then by the bubbles of their exhausts.

Scotty hooted suddenly, four times. Rick turned quickly in time to see a six-foot shark speed past. The tips of the pectoral fins and the second dorsal were darker than the rest of the fish, and Rick identified it as a black-tipped shark. Obviously, the shark was on business of its own, not particularly interested in them. Still, it was curious. The shark was rushing almost straight up.

[Ill.u.s.tration: _Rick turned in time to see a six-foot shark speed past_]

Scotty gripped his arm and pointed. More sharks! Another black tip. And a ten-foot leopard shark! All rushing upward.

The boys watched tensely, and then out of the dimness above something sped down at them, followed by the sharks. It landed in the clear sand just beyond the marine growth. Rick saw a black tip go for it, then the black tip was struck from the side by the big leopard. In spite of his sudden apprehension, Rick couldn't help wishing for his camera.

The sharks rushed again, and the falling object was lifted from the sand by the disturbed water. This time, Rick recognized it. A chicken! It was tied to a length of string from which dangled a lead sinker. The bird was dead, but apparently freshly so. He knew that it was the chicken blood that had brought the sharks--and a giant barracuda! The great fish, a full six feet in length, slashed past the sharks and tore a chunk out of the bird.

The leopard shark made a fast pa.s.s at the barracuda, then turned and snapped at a black tip. Rick gulped. A hole suddenly appeared in the black's side, as smooth as though scooped out of ice cream. And then the other sharks. .h.i.t the wounded black tip.

There were many sharks now, worrying the chicken and the wounded black tip like fierce dogs over sc.r.a.ps of meat. Rick thought, "We'd better get out of here!" He hooted twice at Scotty, the signal to ascend. Scotty motioned to him to retreat. Rick picked up the dumbbell-shaped object.

It was heavy, but not too heavy to handle, and he started a slow retreat along the sand.

The sharks were paying no attention to the boys, but Rick wasn't at all sure that they wouldn't, once the supply of chicken and wounded shark were exhausted. His mind raced. Where had the chicken come from? Whoever had tossed it into the water would have known that the blood would bring sharks. It wasn't a casual toss, either. Not when the chicken had been weighted with a fishing sinker big enough to carry it to the bottom.

Tony and Zircon would never do such a thing. Besides, they had no chickens.