square inch below
atmospheric. That'll put a force of about a ton and a quarter against
the doors, and he won't be able to open them."

Dr. Kent still didn't grasp the fact that Bern was a spy.

"Explain to him, Morgan," MacHeath told the Federal agent. He went on
down the spiral staircase, knowing that Kent would understand and act
in plenty of time.

* * * * *

The door to the tube was standing open. MacHeath slipped on a pair of
the sponge-soled shoes, noticing angrily that Bern hadn't bothered to
do so. He went into the tube and closed the door behind him. Then he
started down the blackness of the tube at a fast trot. Ahead of him,
in the utter darkness, he could hear the click of heels as the
leather-shod Bern moved toward the target end of the long tube.

Neither of them had lights. They were unnecessary, for one thing,
since there was only one direction to go and there were no obstacles
in the path. Bern would probably have carried a flashlight if he'd
been able to get his hands on one quickly, but he hadn't, so he went
in darkness. MacHeath didn't want a light; in the darkness, he had the
advantage of knowing where his opponent was.

Every so often, Bern would stop, listening for sounds of pursuit,
since his own footsteps, echoing down the glass-lined cylinder,
drowned out any noise from behind. But MacHeath, running silently on
the toes of his thick-soled shoes, kept in motion, gaining on the
fleeing spy.

A two-mile run is a good stretch of exercise for anyone, but MacHeath
didn't dare slow down. As it was, Konrad Bern was already tugging
frantically at the door that led to the target room by the time
MacHeath reached him. But the faint sighing of the pumps had already
told MacHeath that the air pressure had been dropped. Bern couldn't
possibly get the door open.

MacHeath's lungs wanted to be filled with air; his chest wanted to
heave; he wanted to pant, taking in great gulps of life-giving oxygen.
But he didn't dare. He didn't want Bern to know he was there, so he
strained to keep his breath silent.

He stepped up behind the physicist in the pitch blackness, and judging
carefully, brought his fist down on the nape of the man's neck in a
hard rabbit punch.

Konrad Bern dropped unconscious to the floor of the tube.

Then MacHeath let his chest pump air into his lungs in long, harsh
gasps. Shakily, he lowered himself to the floor beside Bern and
squatted on his hau