till too far away to see its exact position, or whether there were men
around it.

Rick's heart beat faster, and his breathing speeded up appreciably. In
spite of Zircon's plan to claim they were only checking on the frogmen's
interest in the wreck, Rick knew that being discovered would mean
serious trouble. He recalled Steve's warning that they were up against a
ruthless enemy.

The question was, how close could they get without being seen? He could
take pictures at ten feet, but at any greater distance the camera would
be useless.

Zircon moved ahead, going slowly now. Rick followed, not bothering with
the dark-light unit because the glow in the water was enough for a
beacon. Then the glow faded for a moment as a figure crossed in front of
it. Still Zircon moved ahead until Rick could see two additional,
smaller glows that he identified as the belt lights the frogmen had been
wearing.

Zircon continued on, still hugging the bottom, and Rick divined his
intention. The big scientist was going to take them directly under the
frogmen! It was logical, since the frogmen would not expect danger
below.

Rick followed, staying just behind Zircon's flippers, feeling the wash
of water from his wake. The light was nearly overhead now, and Rick saw
dark figures moving. It was unreal, like a Hollywood motion picture,
except that the tense music of a movie production was replaced only by
the soft sighing of their regulators.

And with the thought, Rick almost lost his mouthpiece. Their bubbles!
Their bubbles would rise right past the frogmen, a dead giveaway! It
might already be too late, because Zircon was almost directly under the
cave!

CHAPTER XII

Clouds Over Clipper Cay

Rick jerked frantically on the tie rope, four times for danger, then he
turned and swam rapidly back the way they had come. At first he felt
resistance on the line, then Zircon hurried to catch up. Not until they
were barely within seeing distance of the light did Rick stop, then he
took his belt slate, started the camera for light, and wrote "Bubbles go
by thm if we undr. They see."

Zircon held a hand to his head in a sign of chagrin that he had
forgotten, then he wrote, "Hw we gt clos?"

Rick pondered the problem. The bubbles had alarmed him in another way,
too. It was possible that the man on the boat could see four sets of
bubbles rising where only two were supposed to be. Yet, he couldn't
escape the feeling that it was important t