Scotty whistled.

Rick laughed. "Quite a story," he said.

"I pointed out the obvious," Tony went on, "that it was strange they should choose a stormy night. Their answer was that storms upset fish, and they thought it possible that some sounds might be obtained only under storm conditions."

"Very interesting," Rick remarked. "It's a good story, and if we didn't know Steve was after at least one of those men, we'd probably believe it!"

"Fish noises!" Scotty exclaimed. "If they knew we'd been snooping around before, they'd probably claim that the octopus really did wail, and that they were only recording him. Your gag about screaming squid and burbling barracuda would appeal to them, Tony."

The archaeologist chuckled. "Anyway, we got out of that one pretty well.

I had a little trouble banging my tank. Didn't want to do it overtly, of course. Finally I managed to get in position while we were swimming to the boat, and I banged my tank against one of theirs. But how did you know what to do?"

Rick explained briefly, then he broke into a smile again. "These guys are smart," he declared. "I like that fish-recording story."

"It's appealing," Tony admitted. "I'm almost tempted to pay them another call tomorrow to ask if they have captured for posterity the hunting cry of the wild sea trout, or the love song of the gay sardine."

"But you won't," Scotty said practically. "You certainly came out of that mess with a whole skin, Tony."

Rick laughed. "He's adventure-p.r.o.ne. And lucky. How do you beat a combination like that?"

CHAPTER XVI

The Deadly Spring Gun

The storm blew itself out by noon of the following day, leaving an overcast sky and heavy swells. An inspection with the binoculars showed that all was quiet at the frogmen's house. Their boat was tied to the pier.

"They probably recovered the bra.s.s ball during the night," Rick observed, "or perhaps early this morning."

"The question is," Scotty remarked, "did they take the gadget to the octopus cave?"

Tony joined them on the porch in time to hear Scotty's query. "I can shed some light on that. It happens that I woke up at dawn and looked out to see how the weather was behaving. The frogmen were anch.o.r.ed off the eastern reef in the same place. We can a.s.sume that they picked up the bra.s.s ball and put it back in the cave near the wreck."

Rick rubbed his hand over his short hair in a gesture of bewilderment.

"But what's their game? What do they get from the bra.s.s ball?"

"I rather imagine Steve Ames would like to know the same thing. If you boys have no objection, I think I'll spend the afternoon at my midden.

What are you planning?"

Rick looked at Scotty. "Dive at the wreck?"

"Sure. Frogmen or no frogmen, there's still a golden statue of St.

Francis somewhere down there."

After lunch the boys checked their equipment, being particularly careful because they had not rinsed out the regulators with fresh water after every dive. Their small supply of water, coupled with the odd hours at which the equipment had been used, was the reason. They took a little water from their supply and used it to clean the regulators. The rest of the equipment would just have to wait.

Tony departed for his Indian midden, tools slung over his shoulder. The boys started the compressor to fill the tanks used the previous night, then untied the _Water Witch_ and headed for the diving area. Scotty scanned the frogmen's house through the gla.s.ses, but saw nothing of interest.

They anch.o.r.ed just outside the reef and looked for their buoy. It was gone, probably torn away by the storm.

"We can find the wreck again," Rick said. "No trouble. I could find my way around here in the dark." He grinned. "I have!"

"Shall we take a look in the octopus cave too?"

"A quick one. I doubt that we'd see more than we saw last night. Our job now is finding out what kind of information the frogmen get. And I don't know how we'll do that."

"Wait for a break," Scotty replied. "Come on. Let's get into the water."

It was cold. The storm had blown in colder water from the open sea. Rick felt goose flesh and wished they had brought along midseason suits.

The water was murky, too, because of the sand and silt stirred up by the storm. The murkiness started about twenty feet below the surface. Not until they were over fifty feet down did the water clear again. The light was reduced somewhat by the murk, but visibility was good. Rick had brought his camera to take motion pictures around the wreck. There would be enough light.

Scotty carried the big jet spear gun. It was powerful enough to spear sharks or big barracuda, just in case the frogmen decided to be "mischievous" again.

Rick led the way to the octopus cave, glancing up now and then to make sure they were alone in the water. The little octopus was in his usual position on the ledge.

Scotty, spear gun extended, swam right into the cave. Rick followed, holding the camera tightly to his chest to keep it from sc.r.a.ping on the coral. Scotty had his flashlight going, so Rick didn't bother with his own.

The cave was just about large enough for both of them. It was a typical coral formation, not much different from the reef outside, except that the bra.s.s ball was in the center of the rough floor.

The boys examined the cave thoroughly and saw nothing of interest. Rick pushed at Scotty's shoulder and swam out again. Scotty followed. The octopus watched them go.

The wreck of the _Maiden Hand_ was just as they had left it, and the grouper was back in his comfortable cabin. He departed at high speed as the boys appeared. They had agreed to start work aft of the captain's cabin, and the wrecking bars were carried under their tank harnesses for the purpose. Both were convinced that there was nothing more to be found in the cabin, although the possibility remained that false boards in the floor or walls might conceal the statue.

Rick tied his camera to a projection, then took his wrecking bar and looked for a place to start. Scotty pointed to a place where there were boards aft of the cabin they had already uncovered, and they started to work.

By the time they had pried off the first few boards it was time to surface. They went topside and changed tanks, then rested for half an hour. There was no sign of activity at the frogmen's house, nor could they see Tony at work on his midden, since the location was hidden by palms.

Rick said thoughtfully, "The bra.s.s ball might be some kind of signaling device."

"What kind of signals?"

He didn't know the answer to that. "Anyway, since it's underwater, if it sends out anything it must be sound impulses. Otherwise we wouldn't hear it wail. And what good is sound if not for signals?" added Rick.

"Sonar," Scotty reminded.

The boys were familiar with sonar because of the Spindrift work on the Submobile. Very high frequency sound impulses were sent out, and the echoes were timed or used in other ways. It was the way in which bottom tracings were made by surface craft, and the way in which Navy ships detected submarines. It could be used for locating schools of fish.

"It could be sonar of some kind," Rick agreed. "But what good would it do anyone to stick a sonar device on an island like this?"

And there speculation stopped again, the question still unanswered.

They dove to the wreck and continued the hard labor of taking the aft end of the ship apart. When they finally got the new area cleared of rotted boards and timbers it was only to find a cabin already filled with sand.

Rick borrowed the spear from Scotty's gun and thrust it down into the sand. It slid in easily, meeting no obstruction. He probed with it but found nothing except more sand.