"Monitoring Services, Wolverton," came a gruff voice.

"This is Dr. Corbett in the Medical Suite. I need you to run a trace on Michele Bishop."

"Can I have your passphrase, Doctor?"

Corbett gave it. The faint sound of keystrokes filtered over the phone. Then Wolverton spoke again. "She's currently in the Environmental Control spaces, deck eight."

"Environmental Control?" Corbett wondered aloud.

"Is there anything else, Doctor?"

"That will be all, thanks." Slowly, thoughtfully, Corbett hung up the phone. Then he picked up his mobile and-stopping just long enough in reception to tell Bryce he was temporarily in charge-left the Medical Suite.

Environmental Control was a large, essentially unmanned warren of dimly lit compartments in a far corner of deck 8. It was filled with furnaces, compressors, humidification systems, electrostatic precipitators, and other devices designed to make the air on board the Facility as comfortable and germ free as possible. Although the floors and walls hummed with the spinning of a dozen turbines, there was remarkably little noise. The watchful, listening silence felt oppressive to Corbett. He opened his mouth to call Bishop's name, but something about that silence made him reconsider. He moved quietly through the first compartment, into a second, and then into a third.

This last space was full of massive air ducts and steel-encased "filter farms" that rose from floor to ceiling. It was even darker than the previous two compartments, and Corbett threaded his way slowly between the ducts, looking from one side to the other. Had Bishop already left? Perhaps the tech in Monitoring had been mistaken and she'd never been here. It seemed a highly unlikely spot, and…

Suddenly, Corbett caught sight of her. She was kneeling before a bulkhead at the far end of the room, back to him, utterly absorbed in something. For a brief moment he thought she must be administering CPR; but then, squinting through the dim light, he realized what he'd thought was a body was actually an oversized black duffel bag. He took a step closer. Strange: her elbows were rocking back and forth as if she were, in fact, performing cardiac massage. Corbett frowned, perplexed. Judging by the faint grunts of effort, whatever she was up to took some doing.

Corbett took another step forward. Now he could see over her shoulder. She was kneading a long, claylike brick, stretching it out into a thick, off-white rope about two feet long.

Two other such ropes had already been pressed against the steel bulkhead in front of her.

Before he could stop himself, Corbett drew in a sharp breath. Instantly, Bishop dropped the puttylike brick and jumped to her feet, whirling to face him.

"You're the saboteur," Corbett said, obviously. "The one who tried to rupture the dome."

Her nostrils flared, but she said nothing.

Corbett knew he should do something-run, call for help-but he felt dazed, even paralyzed, by shock. "What is that?" he asked. "Semtex?"

Still Bishop said nothing.

Corbett's mind reeled. It's true that, despite working with her for months, he really knew very little about Michele Bishop. Even so, it seemed impossible. It can't be, it can't be. Maybe there's some mistake.

"What are you doing?" he asked.

At this, she finally spoke. "I should think that would be obvious. The southern pressure spoke is just on the other side of this bulkhead."

Somehow, hearing her speak-hearing this affirmation of treachery from her own lips-broke Corbett's mental logjam. "The pressure spokes are full of seawater," he said. "You're going to rupture the hull. Flood the Facility."

He took a step backward.

"Stay where you are." Something in her voice made Corbett freeze.

"Why are you doing this?" As he spoke, he put his hands behind his back as casually as possible.

Bishop didn't reply. She seemed to be debating her next move.

Slowly, stealthily, Corbett slipped his cell phone out of his back pocket. He opened it as quietly as possible, then dialed 1231 with the edge of his thumb. It was the extension of his intern, Bryce: a number that could be entered quickly and easily, without looking. He fumbled for the mute switch; not finding it, he moved his thumb over the cell phone's speaker, muffling it.

"We don't have any Composition-4 on this side of the Barrier," he said. "How'd you get it?"

Any indecisiveness had now left Bishop's face. She laughed mirthlessly at the question. "A lot of medical by-products get transported back and forth in the Tub. You know that. The guards aren't too eager to paw through a lot of red-bag waste. It's possible to get all sorts of things through that way. Such as this." And she dipped her hand into a pocket of the lab coat and pulled out a gun.

Corbett, still numb with surprise, looked at the gun with something like detachment. It was an ugly little weapon with an unusual glossy texture and a silencer snugged onto the barrel. He was about to ask how she'd gotten it through the metal detectors, but the glossy look provided an answer: it was a ceramic-polymer composite, expensive and illegal.

"If you flood the Facility, you'll die too," he said.

"I'm setting the detonators for ten minutes. By that time I'll be on deck twelve, headed for the escape pod."

He shook his head. "Michele, don't. Don't betray your country like this. I don't know what country you're working for, but it isn't worth it. This isn't the way."

Bishop's face abruptly darkened. "What makes you think I'm working for a foreign government?" she asked fiercely. "What makes you think I'm working for a government at all?"

"I-" Corbett began, then stopped, taken aback by this sudden outburst.

"The United States can't be allowed to get its hands on what's down there. America has already shown, time and time again, how it abuses the power it's given. We got the atomic bomb, and what did we do? Within six months we'd nuked two cities."

"You can't compare that to-"

"What do you think America will do with the technology that's down there? America can't be trusted with that kind of power."

"Technology?" Corbett asked, genuinely confused. "What technology are we talking about?"

As quickly as the outburst began, it ended. Bishop didn't answer, simply shaking her head angrily.

Into the silence came the squawk of a male voice.

Now for the first time Corbett felt real fear grip his vitals. In the heated exchange he'd forgotten to keep his thumb pressed over the cell phone's speaker.

Bishop's expression hardened further. "Let me see your hands."

Slowly, Corbett raised his hands. The cell phone was in his right.

"You…!" With a sudden movement, fast as a striking snake, Bishop pointed the gun at him and pulled the trigger.

There was a puff of smoke; a sound remarkably like a sneeze; and then a terrible burning sensation exploded in Corbett's chest. A massive force threw him backward against a ventilator housing. He sank to the floor, wheezing and gargling. Just before an irresistible blackness enveloped him, he saw-dimly-Bishop stomp brutally on the cell phone, then kneel again and continue molding the brick of plastique against the outer bulkhead as rapidly as possible.