“I don’t see any alternative. We can’t get that many people out by train or air fast enough. But we can walk.”

“But walk to where?”

“To Libya Station.”

“Sax, it’s about seventy k from Burroughs to Libya Station, isn’t it?”

“Seventy-three kilometers.”

“That’s a hell of a long way to walk!”

“I think most people could manage it if they had to,” he said. “And those who can’t could be picked up by rovers or dirigibles. Then as people get to Libya Station, they can leave by train. Or dirigible. And the station will hold maybe twenty thousand at a time. If you jam them in.”

Nadia thought about it, looking down at Sax’s expressionless face. “Where are these masks?”

“They’re back at Da Vinci. But they’re already stowed in fast planes, and we could get them here in a couple hours.”

“Are you sure they work?”

Sax nodded. “We tried them. And I brought a few along. I can show you.” He got up and went to his old black bag, opened it, pulled out a stack of white facemasks. He gave Nadia one. It was a mouth-and-nose mask, and looked very much like a conventional dust mask used in construction, only thicker, and with a rim that was sticky to the touch.

Nadia inspected it, put it over her head, tightened the thin strap. She could breathe through it as easily as through a dust mask. No sensation of obstruction at all. The seal seemed good.

“I want to try it outside,” she said.

• • •

First Sax sent word to Da Vinci to fly the masks over, and then they went down to the refuge lock. Word of the plan and the trial had gotten around, and all the masks Sax had brought were quickly spoken for. Going out along with Nadia and Sax were about ten other people, including Zeyk, and Nazik, and Spencer Jackson, who had arrived at Du Martheray about an hour before.

They all wore the current styles of surface walker, which were jumpsuits made of layered insulated fabrics, including heating filaments, but without any of the old constrictive material that had been needed in the early low-pressure years. “Try leaving your walker heaters off,” Nadia told the others. “That way we can see what the cold feels like if you’re wearing city clothes.”

They put the masks over their faces, and went into the garage lock. The air in it got very cold very fast. And then the outer door opened.

They walked out onto the surface.