their exhausts, and the
light was subdued and even. It was a world without shadows. Still, Rick
thought, there was plenty of light for photography. Next time he would
bring his camera.

The watch showed him that over half their allotted time was gone, and he
hooted once to Scotty, then reversed course, heading back toward their
floats.

They approached the patch where they had seen the ray and Rick paused
suddenly. There was an odd shape on the sand near the patch. He
flippered over to it and examined it. Scotty joined him. It looked like
an oversized mushroom protruding from the sand at an angle.

Rick unsheathed his knife and poked at it. The sharp tip penetrated for
a fraction of an inch, then stopped. It was either rock or metal, and
judging from the shape, it was unlikely that it was rock. He put his
knife under it and pried, and the thing moved in the sand.

Both boys went to work on it, scooping the sand from around it. In a
moment they had it clear. It was something like a dumbbell, covered with
marine growth where it had been above the sand, but fairly smooth under
it.

Rick took his belt slate and scribbled, "Metal."

Scotty nodded. Then both of them turned to look at the patch of marine
life.

A distant throb, as though of a boat, caught their attention. They
looked up, but the surface was invisible.

It was Tony and Zircon, Rick decided. They probably had returned to the
cottage and found the diving equipment missing. They could spot the
location where the boys were diving easily enough, first by the floats,
then by the bubbles of their exhausts.

Scotty hooted suddenly, four times. Rick turned quickly in time to see a
six-foot shark speed past. The tips of the pectoral fins and the second
dorsal were darker than the rest of the fish, and Rick identified it as
a black-tipped shark. Obviously, the shark was on business of its own,
not particularly interested in them. Still, it was curious. The shark
was rushing almost straight up.

[Illustration: _Rick turned in time to see a six-foot shark speed past_]

Scotty gripped his arm and pointed. More sharks! Another black tip. And
a ten-foot leopard shark! All rushing upward.

The boys watched tensely, and then out of the dimness above something
sped down at them, followed by the sharks. It landed in the clear sand
just beyond the marine growth. Rick saw a black tip go for it, then the
black tip was struck from the side by the big leopard. In spite o