Stone shrugged. "The safeguards . . ."

Hall remembered talking to Burton earlier about the central-core safeguards. In theory, once inside the central core you could go straight to the top. But in practice, them were ligamine sensors located around the core to prevent this. Originally intended to prevent escape of lab animals that might break free into the core, the sensors released ligamine, a curare derivative that was water-soluble, in the form of a gas. There were also automatic guns that fired ligamine darts.

The mechanical voice said, "There are now two minutes forty-five seconds to self-destruct."

Hall was already moving back into the lab and staring through the glass into the inner work area; beyond that was the central core.

Hall said, "What are my chances?"

"They don't exist," Stone explained.

Hall bent over and crawled through a tunnel into a plastic suit. He waited until it had sealed behind him, and then he picked up a knife and cut away the tunnel, like a tail. He breathed in the air of the lab, which was cool and fresh, and laced with Andromeda organisms.

Nothing happened.

Back in the lab, Stone watched him through the glass. Hall saw his lips move, but heard nothing; then a moment later the speakers cut in and he heard Stone say, "—best that we could devise."

"What was?"

"The defense system."

"Thanks very much," Hall said, moving toward the rubber gasket. It was circular and rather small, leading into the central core.

"There's only one chance," Stone. said. "The doses are low. They're calculated for a ten-kilogram animal, like a large monkey, and you weigh seventy kilograms or so. You can stand a fairly heavy dose before—"

"Before I stop breathing," Hall said. The victims of curare suffocate to death, their chest muscles and diaphragms paralyzed. Hall was certain it was an unpleasant way to die.

"Wish me luck," he said.

"There are now two minutes thirty seconds to self-destruct," Gladys Stevens said.

Hall slammed the gasket with his fist, and it crumbled in a dusty cloud. He moved out into the central core.

It was silent. He was away from the sirens and flashing lights of the level, and into a cold, metallic, echoing space. The central core was perhaps thirty feet wide, painted a utilitarian gray; the core itself, a cylindrical shaft of cables and machinery, lay before him. On the walls he could see the rungs of a ladder leading upward to Level IV.

"I have you on the TV monitor," Stone's voice said. "Start up the ladder. The gas will begin any moment."

A new recorded voice broke in. "The central core has been contaminated," it said. "Authorized maintenance personnel are advised to clear the area immediately."

"Go!" Stone said.

Hall climbed. As he went up the circular wall, he looked back and saw pale clouds of white smoke blanketing the floor.

"That's the gas," Stone said. "Keep going."

Hall climbed quickly, hand over hand, moving up the rungs. He was breathing hard, partly from the exertion, partly from emotion.