"Well, if he's on foot, we could send a car out there. We'd get there before he does. Uh ... wouldn't we?" "Maybe. But he'll kill himself if he sees he's trapped." That wasn't quite true. Bern was ready to fight to the death, and he had a heavy pistol to back him up. MacHeath didn't want to see anyone killed, and he didn't want stray bullets flying around the inside of that tube or in the target room. MacHeath and the FBI agent piled out of the elevator at the bottom of the shaft. Dr. Roger Kent was standing at the head of the stairs that spiraled down to the gun chamber. Dr. Kent knew that Bern had gone down the stairway, but he didn't know why. "He's our saboteur," MacHeath said quickly. "I'm going after him. As soon as I close the door and seal it, you turn on the pumps. Lower the air pressure in the tube to a pound per 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.