Rick thought that one over. "We wouldn't have heard the ship until it was very close because of the noise our bubbles make. But we should have heard it about the time it left the reef opening near our cottage. I don't know why we didn't."

"And I don't know why we didn't see it," Scotty added. "It's big enough to be spotted at horizon distance."

Jimmy grinned. "We pulled a fast one. We had enough steerageway to drift over your position after a few turns of the screws down by the reef pa.s.sage. You see, we didn't know what was going on, so we took no chances. Then, when we got into position, we got into the water without waiting to anchor. We dropped anchor right after we got both of you out, but you probably didn't notice."

"I couldn't have cared less, at that point," Rick said, and Scotty echoed the sentiment.

"The reason why you didn't see us coming is that we came from the other side of the island. It's safer for a ship that draws as much water as this one. Tony spotted us as we approached the southern point."

Steve grinned. "Anyway, it's a good idea to move in on an objective as quickly, silently, and invisibly as possible."

"Have you captured the rest of the stations yet?" Rick asked.

"No. But we have teams out, and they know where to go and what to look for, thanks to the man who talked last night."

"Who are these people?" Scotty demanded.

Steve scratched his chin. "Well," he said finally, "you might put it this way: they're people who have no business knowing what they're trying to find out."

Rick hid a grin. He knew perfectly well they would get no more information out of Steve. The essence of security is to give information only to people who have a need to know it. The Spindrifters had no reason for knowing the ident.i.ty of the enemy, apart from their own curiosity. One thing was certain, though, it was another nation that wanted the information.

"You're probably tired of answering questions," Rick said, "but I've got one more. How did you happen to arrive right in the nick of time?"

"Nothing very mysterious about it," Jimmy Kelly answered. "We steamed up to the island and sent a boat ash.o.r.e, with Professor Zircon. Dr. Briotti had seen us approach, and he met the boat. He told us you were diving.

Zircon had a.s.sumed as much since we could see your boat anch.o.r.ed on the reef."

"I told them about last night," Tony added.

"Yes, and we sent a party of men to the house up the beach to capture these fancy frogmen of yours. The house was empty. Since their boat was tied up, we made a quick a.s.sumption that they were out on the reef with you. We did a fast run out ..."

"And got the fright of our lives," Steve finished. "We knew there were three of the enemy and two of you down below, and we could see only three sets of bubbles. We thought you were done for."

"It was remarkable the way Lieutenant Kelly and his men got ready to dive," Zircon said. "I've never seen people move so fast. Steve, too.

Then, just as they were about to go over the side, we saw two more bubble trails and knew at least that you were still alive. But in a moment the entire pack of bubbles merged."

"We hit the water," Jimmy Kelly said, "and were about to dive when one of the enemy skyrocketed up. He was blue in the face and scared witless.

We hauled him out and then started to dive again. And along came Scotty, half dead and babbling about you. I started straight down to get you, but you met me halfway." He grinned. "You weren't in very good shape, either, for a few minutes."

"How about the men? Where are they?" Scotty asked.

"Down below. Locked up, with an armed guard at the door."

Steve Ames finished his coffee and sat back with a sigh of satisfaction.

"I'm happy," he announced.

The boys grinned. He looked it.

"Glad you wound this up so fast," Zircon boomed. "When will you return to Charlotte Amalie?"

Steve looked at Jimmy Kelly. "You in a hurry?"

"Not particularly. Now that this case is over we go back to some pretty dull routine. Why?"

"Oh, I thought your boys might like a little recreation."

Jimmy looked suspicious. "Any sailor likes recreation. The more the better. The UDTs enjoy it more than most. What's on your mind?"

Steve's wave took in the four Spindrifters. "It wasn't their fault one of the gang talked his head off last night. If he hadn't, their work here would have given us a lead we couldn't have gotten in any other way. Suppose we repay 'em."

Jimmy sighed. "Get to the point."

"Keep the ship here tomorrow. Turn your boys loose to help find the treasure they're after. You've got equipment they need. Besides, I'm sure your gang can find some nice souvenirs if they put their minds to it. Old cutla.s.ses, cannon, cannon b.a.l.l.s--things like that."

"It's a deal." The UDT lieutenant chuckled. "I'll try a little souvenir hunting myself. Of course, since it's unofficial, I'll have to ask for volunteers."

"Think you'll get many?" Rick asked anxiously.

Steve and Jimmy laughed. The lieutenant said with a chuckle, "If one of them doesn't volunteer I'll turn him over to the doctor, because I'll know he's sick. The UDT's volunteer because they like to swim. It isn't often they get a chance like this, to dive just for fun."

"If we don't find the treasure," Scotty said with satisfaction, "it'll be because it isn't there!"

CHAPTER XX

The Buried Secret

At first, the captured frogmen were defiant. They insisted that the Navy had nothing on them. The bra.s.s ball wasn't theirs. They were only sport divers having some fun.

Then, faced with the una.s.sailable fact that Rick had taken motion pictures of their activities, they lapsed into sullen silence and refused to talk.

Rick and Scotty watched Jimmy Kelly check the diving equipment of the frogman teams lined up on the destroyer escort's deck. Beyond the teams they could see the three enemy frogmen, taking the air under the watchful eye of a shotgun-armed sailor.

"I wonder if we'll ever get the full story," Rick mused.

"We've got all we need," Scotty answered. "What pieces are missing?"

"Well, I'm curious about the chicken. I think we hit it when we decided they wanted to scare us out of the octopus-cave area, but it would be nice to know for sure. And why did they take the sonar equipment to the eastern reef during the storm?"

"Probably to make a recording as a routine check. They couldn't a.s.sume all sub activity was taking place to the west."

"But how can we be sure?"

"We can't. We can only try to figure out what happened, based on what information we have. For instance, there must have been a sonar unit near where we swam at St. Thomas. It's the only thing that could have got the shadow so excited. But what difference does it really make? We know most of the story, and we can guess the rest."

"Steve may be able to fill in some pieces later," Rick observed. He liked to have a thing wrapped up neatly, with no loose ends hanging.

Still, that was almost impossible in a case like this.