Ten minutes later the scientists surfaced, and Rick helped them aboard.

Tony removed his mask and grinned. "It's as wonderful as you said it was."

"What kind of ship was it?" Rick asked.

Tony had been a destroyer skipper during the war and he knew ships.

"Probably an interisland cargo carrier of some kind. At any rate, it appears to be a small cargo ship. It's so overgrown with marine growth that the shape is cluttered. It might have been a small tanker."

"We can explore it from stem to stern," Rick suggested excitedly.

Scotty joined them and commented, "But not right now. We'll have to go ash.o.r.e and charge the tanks. There may be time for one more dive this afternoon if we hurry."

"Besides," Hobart Zircon said with a smile, "I'm hungry. As you say, Rick, diving certainly develops the appet.i.te!"

They docked, and Tony and Zircon went off to see about preparing sandwiches. The boys decided that rather than carry the tanks back and forth from the pier to the shed, it would be more sensible to bring their small, portable gas-driven compressor to the pier.

Scotty went after it while Rick tied the tanks to the afterrail of the _Water Witch_, in position for filling.

A yell from Scotty stopped him. He looked up and saw his friend beckon, and ran down the pier to the house. The scientists joined him and Scotty at the shed where the compressor had been stored.

"We've been sabotaged again," Scotty told them flatly. "There's oil in the compressor!"

"Are you certain?" Zircon pressed close to examine the machine.

"Yes. I stumbled over my own feet and tipped the compressor on its side.

And oil ran out through the air fitting. Look!" Scotty held up his hand, and it was smeared with glistening oil.

A cold shiver traced its way down Rick's spine. Oil in a compressor was blown into fine particles, too small to be seen. If they got into an air tank they would be breathed in, leaving a thin coating on a diver's lungs. The result was a condition almost exactly like pneumonia, called "lipoid pneumonia." Their special filter, designed by Zircon, probably would have taken all the oil particles out of the air before it got into the tanks, but that didn't alter the fact that faced them. Someone had deliberately put oil in the compressor. Someone just didn't want them around!

CHAPTER VIII

The Fancy Frogmen

"The question is," Rick stated, "when was the oil put in? While we were at Charlotte Amalie? Or while we were out hunting the wreck just now?"

"In Charlotte Amalie, of course," Tony said. "Why do you think it might have been done just a little while ago?"

Rick shrugged. He had no answer to that. The question had popped into his mind unbidden.

"We didn't take the compressor apart," Scotty reminded him.

That was true. But Rick had started it in Charlotte Amalie to be sure it was functioning. There was no oil in it then. He said as much.

"You started the compressor at the same time you checked the tanks,"

Zircon reminded him. "I believe the oil was put in at the same time the valves were loosened."

That seemed reasonable. Rick put aside his hunch. "Well, we found it in time, anyway. Now Scotty and I will have to tear the compressor down and clean it before we can recharge the tanks."

"After lunch," Tony said. "Don't you remember? A diver is supposed to rest after each dive. Relax, and I'll have some sandwiches ready in a few minutes."

All hands were hungry. Scotty stowed away four sandwiches and Rick did nearly as well. Then they started work on the compressor. It wasn't a hard job, but it was tedious, and nearly two hours elapsed before they finished. Each part had to be washed in soap and water, then carefully dried. Finally, the compressor was ready. They carried it to the boat, started the gas engine, and connected the tanks. But before the air started to flow, Rick carefully inspected the filter system to be sure that hadn't been tampered with too.

"You know," he observed, "these enemies Steve is hunting know a lot about sport diving."

Scotty considered. "They knew that tanks could be dangerous, and they knew that oil in a compressor is dangerous. You're right, Rick. They know plenty about it."

"But it doesn't do us much good to know that they know," Rick concluded.

"Well, now what? It will be a few hours before all the tanks are charged."

"Where are Zircon and Tony?"

"Napping. We probably should join them."

"Not me. There's nothing to do after sundown but sleep. I'd like to take a walk and look the island over."

Rick sighed. "Always an eager beaver. I'll go with you, if you don't walk fast."

They turned north and walked up the beach. Somewhere off this stretch of beach was the _Maiden Hand_. But where? They strolled along leisurely, stopping now and then to examine some bit of beach flotsam. There were sh.e.l.ls, but most of them were small and water worn.

"We'll have to collect a few sh.e.l.ls on the reef," Rick said. "Barby will be disappointed if we don't."

"That's easy enough to do," Scotty replied. "I saw half a dozen different varieties this morning."

They pa.s.sed a beach house, obviously empty. Rick gestured toward it.

"Funny how few people there are here. If I owned a place on this island I'd be here all the time."

"Unless you had to make a living," Scotty added practically. "This isn't the season for vacations. I expect vacation time finds plenty of activity here. There's one cabin occupied to the south of us. I saw people there this morning. They're probably the same ones who waved at us from a boat when we flew over day before yesterday."

"The boat isn't there now," Rick observed. "At least, I haven't seen it."

"They may have gone to St. Thomas for supplies. Or they may have gone home." Scotty pointed to what seemed to be the largest house on the island, near the northern tip. "That's quite a place. Let's go have a look."

There was a long pier in front of the house, and, unlike the others on the island, this house had a second story. There was no sign of life.

They walked around it and found a barbecue pit. Scotty examined it.

"This has been used recently, probably in the past few days."

Rick bent down and peered at a sc.r.a.p of meat. "You're right. They had steak. And this piece hasn't dried out yet."

"Maybe they're still here." Scotty walked to the back of the house.

"They might be out fishing or something." He looked in a window and called urgently, "Rick! Look!"

Rick hurried to his side and peered in. The room was evidently used for storing diving equipment. Hung along one wall were three full diving suits of expensive make. Next to them, neatly racked, was an a.s.sortment of spear guns, all of the spring type, and all of Italian make.

On another wall were three Scuba regulators, not aqualung types such as the boys used, but the variety that carries a full face mask through which the diver breathes. In a rack on the floor were nine spare tanks and a compressor much larger and more expensive than theirs.