spite of his high rate of metabolism, the Nipe can store a tremendous
amount of oxygen in his body, and can stay underwater for as long as half
an hour without breathing apparatus--if he conserves his energy. When he's
wearing his scuba apparatus, he's practically a self-contained submarine.
The pressure doesn't seem to bother him much. He's a tough cookie."

Stanton nodded silently and slowly. Could he beat the Nipe in hand-to-hand
combat? There would be no way of knowing until the final moment of success
or failure.

"At that time," the colonel went on, "we hadn't formulated any definite
policy on the Nipe. We didn't know what he was up to; we weren't even sure
he was actually down in those tunnels. We had to find out."

He walked over to the nearby table and opened a box some twelve inches
long and five-by-five inches in cross section.

"See this?" he said as he took something out.

It looked like a large dead rat.

"Our spy," said Colonel Mannheim.

* * * * *

The rat moved along the rusted steel rail that ran the length of the huge
tunnel. To a human being, the tunnel would have seemed to be in utter
darkness, but the little eyes of the rat saw its surroundings as faintly
luminescent, glowing from the infra-red radiations given out by the
internal warmth of cement and steel. The main source came from above,
where the heat of the sun and of the energy sources in the buildings on
the surface seeped through the roof of the tunnel.

On and on it moved, its little pinkish feet pattering almost silently on
the oxidized metal surface of the rail. Its sensitive ears picked up the
movements and the squeals of other rats, but it paid them no heed. Several
times, it met other rats on the rail, but most of them sensed the
alienness of _this_ rat and scuttled out of its way.

Once, it met a rat who did not give way. Hungry, perhaps, or perhaps
merely yielding to the paranoid fury that was a normal component of the
rattish mind, it squealed its defiance to the rat that was not a rat. It
advanced, baring its teeth.

The rat that was not a rat became suddenly motionless, its sharp rodent's
nose pointed directly at the enemy. There came a noise, a tiny popping
hiss, like that of a very small drop of water striking hot metal. From the
left nostril of the not-rat, a tiny glasslike needle snapped out at bullet
speed. It struck the advancing rat in the center of the pink tongue that
was visib