lunged back into the
grove, almost burying itself in the sandy soil.

The boys sat down and stared weakly at each other. For the first time,
Rick noted that Scotty's hand was bleeding. He said shakily, "Here, let
me look at that."

The scientists rushed out of the house and demanded to know what had
happened. The tank had blown through its devastating course so fast that
they had not even had time to get outdoors.

Zircon bandaged Scotty's hand with supplies from the first-aid kit while
the boys told them what had happened. Tony said, "Very careless, leaving
a valve loose like that."

Rick told him positively, "It wasn't left unscrewed, Tony. We always use
a wrench on those valves because high pressure is so dangerous. And it
wasn't like that yesterday. I checked the tanks when we stowed them on
the boat."

Scotty gestured toward the other tanks. "Better take a look."

Rick did so, and gave a low whistle. The valves had all been loosened.
They were in place only by a turn or two of the threads.

"They could have come out any time," he said grimly. "Any rough handling
could have knocked a valve out. And if it had happened on the boat, the
tank would have gone right through the bottom or side. It was just luck
Scotty and I weren't killed."

Zircon wordlessly found the valve wrench and got to work screwing the
assemblies back in place. The others watched silently, until Scotty
said, "Well, at least we're out of St. Thomas. There won't be any more
sabotage!"

CHAPTER VII

The Derelict

Rick and Scotty were up at dawn the next morning. They didn't bother
with anything so prosaic as breakfast. Instead, they collected masks,
snorkels, and flippers for a preliminary dip. They didn't use the lungs;
those were to be saved for more important work than casual swimming.

For this first swim, each boy selected a spear gun. Scotty chose the
same light spring gun he had used to save them from the shadow, while
Rick took his favorite gun, a four-strand rubber-powered weapon that
packed a terrific wallop. They belted on their knives and blew up their
plastic floats. These were essential for resting, if necessary, and for
bringing home their catch, if any. Once a fish was speared, it was
important to get it out of the water as soon as possible, since blood
would bring sharks or barracuda if any were in the neighborhood.

"Come on," Rick said impatiently. "Let's go."

"I'm coming." Scotty finished coiling up the l