e of you two. I do not need you any longer."

Larry made a last wild jab with his fist into Tugh's face and tried to
twist himself aside. The blow landed upon Tugh's jaw, but the cripple
did not seem to feel it. He stuffed the struggling Larry like a bundle
into the aperture. Larry felt his clutching hands torn loose. Tugh
gave a last, violent shove and released him.

Larry fell into blackness--but not far, for soon he struck water. He
went under, hit a flat, stone bottom, and came up to hear Tina fall
with a splash beside him. In a moment he regained his feet, to find
himself standing breast-high in the water with Tina clinging to him.

Tugh had disappeared. The aperture showed as a narrow rectangle some
twenty feet above Larry's head.

They were within the dam. They were in a pit of smooth, blank,
perpendicular sides; there was nothing to afford even the slightest
handhold; and no exit save the overhead slit. It was a part of the
mechanism's internal, hydraulic system.

* * * * *

To Larry's horror he soon discovered that the water was slowly rising!
It was breast-high to him now, and inch by inch it crept up toward his
chin. It was already over Tina's depth: she clung to him,
half-swimming.

Larry soon found that there was no possible way for them to get out
unaided, unless, if they could swim long enough, the rising water
would rise to the height of the aperture. If it reached there, they
could crawl out. He tried to estimate how long that would be.

"We can make it, Tina. It'll take two hours, possibly, but I can keep
us afloat that long."

But soon he discovered that the water was not rising. Instead, the
floor was sinking from under him! sinking as though he were standing
upon the top of a huge piston which slowly was lowering in its
encasing cylinder. Dimly he could hear water tumbling into the pit, to
fill the greater depth and still hold the surface level.

With the water at his chin, Larry guided Tina to the wall. He did not
at first have the heart to tell her, yet he knew that soon it must be
told. When he did explain it, she said nothing. They watched the water
surface where it lapped against the greasy concave wall. It held its
level: but while Larry stood there, the floor sank so that the water
reached his mouth and nose, and he was forced to start swimming.

Another interval. Larry began calling: shouting futilely. His voice
filled the pit, but he knew it could