ssionals. 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-class
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 cockpit 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 assigned a pair of husky Shore 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 wi