"I'm with you. Go ahead."

"Well, at this point I get lost. You put on your gear and swam out, not with any particular destination in mind, but looking for a rock or a coral head or something of the kind where you could see fish. The shadow watched you. Suddenly he got excited, grabbed a boat, and tried to run you down."

Steve grinned at the boys. "In fact, he got so excited that he stole a boat right out from under the owner's nose. What do you think of that?"

Rick scratched his head. "We'd about decided he was either desperate or stupid. I guess he was both."

Kelly continued. "The big point is, what made him desperate? It could only have been one thing, as I see it. You were getting close to something, and he was afraid you'd find it. So he lost his head. That's borne out by the remark his pal made last night, that he'd pulled enough stupid stunts for one day."

"But what could we have been getting close to?"

"I don't know. Whatever it was, it isn't there now."

Scotty and Rick sat up straight. Scotty demanded, "How do you know?"

Steve smiled. "Because a team of Navy frogmen went over the entire area inch by inch this morning."

At the boys' surprised looks, Kelly explained, "You told the Sh.o.r.e Patrol enough to get us interested. We put teams in the water at daylight. There's nothing there."

"But there could have been," Scotty pointed out. "If they suspected we knew about it, they could have removed it yesterday afternoon or last night."

"Correct," Steve agreed. "They were worried, too. Otherwise why the call on you last night? And the questions?" Steve paused while the waiter served them. "The conclusion is this: Something they value was in the water near where you swam. You met me yesterday morning, and they had already identified me. Which means that they must have agents in Washington who warned them JANIG was moving in on the case. Since it's no secret that I'm with the outfit, they could peg me easily. When you swam out toward this object, whatever it was, they were convinced that somehow JANIG had learned about it. The tail got desperate and tried to knock you off. Then, last night, they tried to find out what you knew, and how."

"Who are 'they'?" Rick asked.

"If I knew that, I'd wrap the case up and go home. Jimmy has been working on it for a week, but he hasn't any answers yet. I've been here twenty-four hours, and I know even less."

"Could you identify the two men?" Scotty queried.

"Yes. Both small fry, both local. And both are obviously green at this kind of business, otherwise you'd be a pair of real cold turkeys by now."

That was true, Rick knew. Experienced agents wouldn't have given him and Scotty the chances that they'd seized.

"The men must know what was under the water," Scotty said.

"Not necessarily. They just knew it was important, and they may have been ordered to protect it. But your former shadow was on the griddle all night, and told all he knew. It wasn't much. He didn't even know who had hired him. He wasn't stalling, either."

"What's the next step?" Rick wanted to know.

"Jimmy and I will drive you to the plane. Then you take off for Clipper Cay. And stay there until your vacation is over. Have you a short-wave radio, by the way?"

"Yes. Why?" Rick had an all-wave battery portable.

"Monitor the Navy command frequency. Here, I'll write it down for you.

Listen every night at six for five minutes. If I want you, I'll send a message. I don't think I will, but it won't do any harm to set up a schedule."

Steve lowered his voice. "Now listen to me. This thing is big. The two you ran up against yesterday were not good samples. We're dealing with some tough professionals. I don't know who they are, but from what I've seen I can tell you they're dangerous. So you two are to stay out of this case. That is an order. Stay on Clipper Cay and have fun."

"I can add a small note to that," Lieutenant Kelly said. "I'm new here.

I was ordered down from Norfolk only a week ago. A first-cla.s.s intelligence officer had my job. He turned up in a hospital in the British Virgins after being missing for two days. He had a fractured skull. He still doesn't know what happened to him, and neither do we."

"Okay," Steve said flatly. "I appreciate the way you handled things yesterday, but that's the end so far as you are concerned. Get out, and stay out! And that's final!"

CHAPTER VI

The Deadly Tank

The Sky Wagon droned smoothly through a series of figure eights as Rick and Scotty inspected every inch of Clipper Cay and its surrounding waters. While Rick flew, Scotty marked off landmarks on the chart of the island that Dr. Ernst had provided.

"I wish we could spot the wreck of the _Maiden Hand_," Scotty remarked.

"Too deep," Rick said. "We can't see bottom at twenty fathoms even in water as clear as this."

"I've got everything important marked. What say we land and look over our property?"

"Okay. I'll shoot the beach while you look for coral heads. We don't want to snag a pontoon."

The boys had already identified their house. It was set at the edge of the palms, about fifty yards inland from the beach. It looked fine.

There was a small dock to which the _Water Witch_ could be tied up when the scientists arrived.

Rick estimated that Tony and Zircon would arrive about sundown, two hours hence. The boys had flown over the _Water Witch_ en route from St.

Thomas. Apparently the scientists were enjoying the trip. Zircon had been sprawled in the c.o.c.kpit while Tony trolled for fish.

"I'm a little surprised there wasn't something wrong with the plane,"

Rick observed. He and Scotty had gone over the Sky Wagon from propeller hub to rudder, fearful that the unknown enemy might have sabotaged the plane. But there was no sign of any tampering. However, the inspection had taken so long that it was late afternoon before they got away. It was significant and perhaps a little ominous that Steve and Jimmy Kelly had a.s.signed a pair of husky Sh.o.r.e Patrol men with .45-caliber sidearms to stay with them until the plane actually took off.

"Maybe the two men who came after us were acting without orders," Scotty replied. "Maybe the real brains of the gang aren't even interested in us."

"I hope that you're right. See any coral heads?"

Although most coral growth was limited to the reef area, outcroppings of coral called "heads" had grown up toward the surface in some places.

There were none in the stretch of water before the beach house where Rick planned to land.

"The water's clear. Pick your direction. There's not enough wind to make any difference."

"I'll land parallel to the beach."

Rick turned south down the center of the island. When he had reached the right position he cut the throttle, and the nose of the Sky Wagon dropped. He banked tightly, reversing course, until the plane was headed north a hundred yards out from the beach. He let the plane feel its way toward the water, then felt the first b.u.mp as the pontoons touched. In a moment they were down, and Rick swung the plane to taxi in toward their new home.

Scotty was already stripping off his shoes and socks. As the pontoons touched bottom a few yards from sh.o.r.e, Scotty climbed out. Rick cut the gun while his pal pulled the plane up on the beach.

Rick got out and waited until Scotty slipped his shoes on again, then they walked to the cottage.

The door was unlocked. Few people came to Clipper Cay, and locks weren't considered necessary. The boys pushed open the front door and walked in.