Her voice was without inflection, like an automaton’s, her face a frozen mask. “Nanomachines could be made to take carbon dioxide out of the atmosphere, can’t they? Break the molecules down into carbon and oxygen atoms. The carbon could be buried, the oxygen released back into the air or sold as an industrial gas, whatever. That could stop the greenhouse warming in a year or two!” Cardenas’s expression did not change. “Nanotechnology is banned, you know that. No matter how you want to use it, you can’t make nanomachines anywhere on Earth. You’d have the GEC, the world government, every religious nut on Earth going crazy if you even hinted that you’re thinking of using nanotechnology.” Humphries smiled patiently. “We won’t tell them, for god’s sake. We just start doing it. In secret. Out in the Sahara or the middle of the ocean or Antarctica, anywhere. In a year or maybe even less, they’ll start noticing the carbon dioxide levels going down. We can take out the other greenhouse gases, as well. They’ll see that the greenhouse warming is lessening. Then we’ll have them all by the balls! They’ll have to accept what we’re doing. They’ll have no choice.”

“And what happens if these nanomachines don’t work exactly right? What happens if they start taking other carbon compounds apart? Like you, for instance. You’re made of carbon atoms, aren’t you?”

“That won’t happen.”

“I know it won’t happen,” she said. “Because I won’t do it. It’s an absurd scheme.”

“What’s absurd about it?” Humphries demanded.

A slight, sardonic smile cracked Cardenas’s facade. “You don’t have any idea of how enormous Earth’s atmosphere is. Do you know how many tons of carbon dioxide you’d have to remove? Billions! Tens of billions, at least! You’d have to cover Africa with nanomachines to remove that much carbon dioxide!”

“I’m sure that’s an exaggeration,” Humphries muttered, scowling. Cardenas shot to her feet, startling George. “All right, you’d merely have to cover the Sahara desert. It’s still beyond belief!”

“But-”

“And you’d never be able to keep it secret. Not a program of that scale.”

“But it could be done, couldn’t it?”

“It could be started,” she admitted. “Until some fanatic drops a nuke on us. Or laces our drinking water with plague bacillus.”

“I can protect you against terrorists,” Humphries said. Cardenas paced to the window, obviously thinking furiously. Turning back to Humphries, she said, “Using nanomachines on that scale is an invitation to disaster. Some fruitcake could steal a handful and re-program them to take apart… plastics, for example. Or petroleum. Or use them as assassination weapons. You’re talking about gobblers, for Christ’s sake!”

“I know that,” Humphries said coldly.

Cardenas shook her head. “It won’t work. Aside from the sheer physical scale of the project, the authorities on Earth would never grant approval for using nanomachines. Never! And I can’t say that I’d blame them.” Humphries slowly got to his feet. “You refuse to even try?”

“It’s a hopeless task.”

He sighed theatrically. “Well, I’ve tried to be reasonable. I thought we might be able to work something out.”

“Let me go,” Cardenas said, with a pleading note in her voice. “I thought it would be a way for you to be with your grandchildren, as you want to be.”

“Just let me go.”

He gave her a sad look. “You know I can’t do that. It’s too great a risk for me.”

“You can’t keep me here forever!”

With a small shrug, Humphries asked, “What do you propose as a way out of this impasse?”

She stared at him, open-mouthed.

“I mean, you can see my problem. I know you can. How can I let you go when there’s every chance that you’ll tell people that I’m responsible for Dan Randolph’s death?”

“But I’m responsible, too.”

“Yes, I know. But you’d confess to it, wouldn’t you?”

“I…” she hesitated, then said in a low, defeated voice, “I suppose I would, sooner or later.”

“There you are,” Humphries said softly. “The problem remains.”

“You’re going to have to kill me.”

“I don’t want to do that. I’m not a cold-blooded murderer. In fact, I’d like to see you reunited with your grandchildren, if it’s at all possible. There must be some way we can work together, some way we can find around this problem.”

“I don’t see any,” Cardenas whispered.

“Well, think it over,” Humphries said, heading for the door. “I’m sure you can come up with a solution, if you just put your mind to it.” He smiled as he opened the door and left. George saw the guard standing out in the hallway before Humphries closed the door and its lock clicked shut. As he strode down the hallway, Humphries mused to himself, It could work! If we could spread enough nanomachines I could break the greenhouse warming in a couple of years. They’d be on their knees with gratitude. He decided to put a small team of experts together to study the possibilities dispassionately. Cardenas isn’t the only nanotechnology guru in Selene, he assured himself.

Kris Cardenas stared at the locked door for several silent moments after Humphries left, then she suddenly broke into racking sobs. Face buried in her hands, body bent, she stumbled to the bed and threw herself onto it, crying inconsolably. George stood uncertainly in the far corner of the bedroom, wondering what he should do. She’s already hysterical, he said to himself. If I go and tap her on the shoulder and say, “Hi! I’m an invisible man!” she’ll probably freak out altogether.

So he waited, fidgeting unhappily, until Cardenas stopped crying. It didn’t take long. She sat up on the bed, took a deep breath, then got to her feet and went to the lavatory. When she came out again, it was obvious to George that she had washed her face and put on some makeup. But her eyes were still red, puffy. Well, you can’t stand here like a fookin’ idiot forever, George told himself. Do something!

Before he could decide what to do, Cardenas walked to the window and pressed her fingers against the glass. Then she turned and seemed to survey the room. With a slight nod, she walked to the bare little desk and picked up its wooden, cushioned chair. It seemed heavy for her, but she carried it, tottering slightly, to the window.

She wants to crash the window and jump out of here, George realized. She’ll just end up hurting herself.

He touched her arm lightly and whispered, “Excuse me.” Cardenas flinched and let the chair thump to the carpeting. She blinked, stared, saw nothing. “Excuse me, Dr. Cardenas,” George whispered. She spun around in a complete circle, eyes wide. “Who said that?”

George cleared his throat and replied, a little louder, “It’s me, George Ambrose.

I’m—”

“Where the hell are you?”

George felt slightly embarrassed. “I’m invisible.”

“I’m going crazy,” Cardenas muttered. She sank down onto the chair, right there in the middle of the room.

“No you’re not,” George said, still keeping his voice low. “I’m here to get you out of this place.”

“This is a trick.”

“Is this room bugged? Do they have any cameras in here?”

“I… don’t think so…”

“Look,” George said, then immediately realized it was a foolish term to use. “I’m gonna take off me hood so you can see me face. Don’t get scared now.” Cardenas looked more suspicious than frightened. George yanked the hood off his head and pulled off his face mask. It felt good to feel cool air on his skin. She jumped out of the chair. “Christ almighty!”

“No, it’s just me,” he said, with a slight grin. “George Ambrose. I work for Dan Randolph, y’know.”

Comprehension lit her eyes. “Walton’s stealth suit! He didn’t destroy it, after all.”

“You know about it.”

“Me, and four other people.”

“There’s a few more now,” George said.