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"I never thought that would involve genocide."

"We’re still not certain that it would."

She sighed, bodily. "So you’re afraid that if we find a natural explanation for the signaling layer, my presence might suddenly become embarrassing?"

"Wouldn’t it?"

"I voted for the moratorium," she said. "I voted to do nothing but look for signs of life, for a full year. Whatever happens, I’ll honor that commitment."

Tchicaya experienced a twinge of shame, but he didn’t back off. He said, "Make up your mind. Are you here to protect the far side? Or are you here to relaunch the Planck worms in a year’s time, if the far side proves to be sterile?"

Mariama shook her head. "Why do I have to choose? If there are sentient creatures in there, they deserve our protection. If there’s nothing but an exotic ocean full of different kinds of Planck-scale algae, then the sooner it’s rendered safely back into vacuum, the better. Is that distinction really so hard to grasp? What did I ever do to get lumped in with the rebels, in your head? When’s the last time I displayed nineteenth-century morality?"

"Twenty-third."

"That just shows how little history you know. Most people who left Earth in that era did so precisely because they were out of step with contemporary mores. In this case, I’d say they were about four centuries behind the times."

Tchicaya looked away. Was she protesting too much? But she was just as entitled as he was to be contemptuous of the anachronauts' views. Being wise after the fact about the complexity of the far side, and the unwitting genocide the Preservationists might have committed, was like blaming the Mimosans for failing to anticipate the failure of the Sarumpaet rules.

The probes began returning. The Planck worms they revealed were dauntingly complex structures, at least as elaborate as the vendeks themselves. And Mariama had been right: they’d begun to mutate, to try out variations. The software counted thousands of strains.

Even if they were capable of adaptation, though, they were too simple to achieve it through anything but trial and error. Their designer had left them to fend for themselves, and in the end that would leave them as vulnerable as any other dumb pathogen.

Tchicaya addressed the toolkit, allowing Mariama to listen in. "Find a graph we can scribe that will wipe these things out — without moving deeper and damaging the native vendeks." As he spoke the words, this sounded like a breathtakingly optimistic request, but the Planck worms themselves had been seeded from a single point, so there was no reason why the antidote couldn’t be introduced the same way.

There was a perceptible delay while the toolkit explored the problem. "I don’t believe that’s possible," it declared. "The Planck worms are exploiting the ordinary vacuum behind them: they set up correlations across the border that cause the vendeks to decohere. I’m unable to find a method of attacking the Planck worms that wouldn’t also destroy the whole vendek population in which they’re immersed."

Mariama said, "What if the vendek population changes, deeper in?"

"Anything might be possible then, but until I know the details, there are no guarantees."

Tchicaya scribed probes to look deeper.

The second change swept the border as swiftly as the first. Through the windows of the shuttle, they saw the smooth gray plain transformed into a complex, striated pattern of dozens of bright hues. Tchicaya’s heart raced; it was like watching a pool of acid eat its way down through featureless rock, exposing thousands of delicately layered sediments.

Mariama said, "The border must be motionless again, or we’d see the pattern changing. So the Planck worms have hit more obstacles. We might have killed them off, if we’d burnt away this whole layer first."

"Including whatever it contained," Tchicaya countered. "We have no idea what might have been there."

Mariama replied flatly, "Whatever was there, it’s gone now anyway."

Tchicaya said nothing, but she was right. If he’d acted more swiftly, they might have cauterized the wound. If he was going to refuse to make decisions with imperfect knowledge, he might as well give up intervening and simply leave the far-siders to protect themselves.

The Left Hand had launched fresh fireflies immediately, but he wasn’t going to wait for them. He told the shuttle to follow them down, keeping just enough distance to be sure it could decelerate in time.