y sloping ramp. The gate descended behind him.

Happy did not know whether Shadow had come through the open gate with
him, but it didn't matter. Shadow could slip easily through the bars
when he wished.

At the foot of the ramp was a vast, low cavern, stretching out of sight
in all directions. It was dim, shading into the darkness of distance.
Its floor was water, flat water, subdivided into large rectangular vats.
In most of the vats vegetation grew in various stages, greening under
the ultraviolet rays that radiated from the low roof. Between the vats
ran straight, narrow walkways of packed earth.

Happy waddled along one of the walkways until he found an empty vat. He
lowered himself over its edge and sank happily into the still, cool
water, like a hippopotamus submerging. He immersed himself completely,
then lay back in the water, with only his face floating barely above the
surface.

Shadow appeared, apparently out of nowhere, and sat down on the edge of
the vat, letting his flat legs dangle into the water.

"Nothing like it," proclaimed Happy, splashing a little. "Nothing on
Mars like it. You ought to come on in, Shadow. As flat as you are, you
ought to float on the surface without any trouble at all."

Shadow nodded silently, but made no move.

"I don't see why the Toughs can't take care of their own barracks,"
complained Happy, returning to the subject closest to his displeasure.
"You reckon the Toughs are actually the rebels, and the Masters can't
make them do anything?"

Shadow shook his head, but whether in negation or disclaimer of
knowledge, Happy could not interpret.

Happy flinched, and shifted in the vat.

"There's still part of a skeleton in here," he announced. "I thought
this was an empty one."

Moving, he flinched again. With purpose, he aroused himself and ploughed
to the edge of the vat.

"I've got to find another vat," he said. "I can't take a nap if I'm
going to get punched in the fanny with bones every five minutes."

He heaved himself over the edge onto the walkway with difficulty, and
got slowly to his feet. Shadow lifted his feet out of the vat, stood up
and vanished.

Happy knew how Shadow was able to disappear so suddenly, and it did not
disturb him. Seen directly from front or rear, Shadow had the dimensions
of a normal, black-skinned man. But Shadow was flat, no thicker than
half an inch. When Shadow turned sidewise, he vanished to the sight.

Occasionally, Happy wonder