Prax nodded. A stab of horror and grief went through him. She wasn’t four anymore. Mei’s birthday had been the month before, and he’d missed it. She was five. But grief and horror were old companions by now. He pushed the thought aside.

“I’ll be clearer,” he said. “Mei’s body isn’t fighting its situation. That’s her disease, if you think about it. There’s a whole array of things that happen in normal bodies that don’t happen in hers. Now you take one of the things, one of the creatures. Like the one from the ship?”

“That bastard was pretty active,” Amos said.

“No,” Prax said. “I mean, yes, but no. I mean active on a biochemical level. If Strickland or Merrian or whoever is using the protomolecule to reengineer a human body, they’re taking one complex system and overlaying another one. We know it’s unstable.”

“Okay,” Naomi said. She was sitting beside Amos and across the table from Holden. “How do we know that?”

Prax frowned. When he’d practiced making the presentation, he hadn’t expected so many questions. The things he’d thought were obvious from the start hadn’t even occurred to the others. This was why he hadn’t gone in for teaching. Looking at their faces now, he saw blank confusion.

“All right,” he said. “Let me take it from the top. There was something on Ganymede that started the war. There was also a secret lab staffed with people who at the very least knew about the attack before it happened.”

“Check,” Alex said.

“Okay,” Prax said. “In the lab, we had signs of the protomolecule, a dead boy, and a bunch of people getting ready to leave. And when we got there, we only had to fight halfway in. After that, something else was going ahead of us and killing everyone.”

“Hey!” Amos said. “You think that was the same f**ker that got into the Roci?”

Prax stopped the word obviously just before it fell from his lips.

“Probably,” he said instead. “And it seems likely that the original attack involved more like that one.”

“So two got loose?” Naomi asked, but he could see that she already sensed the problem with that.

“No, because they knew it was going to happen. One got loose when Amos threw that grenade back at them. One was released intentionally. But that doesn’t matter. What matters is that they’re using the protomolecule to remake human bodies, and they aren’t able to control it with perfect fidelity. The programming they’re putting in fails.”

Prax nodded, as if by doing it he could will them to follow his chain of reasoning. Holden shook his head, paused, and then nodded.

“The bomb,” he said.

“The bomb,” Prax agreed. “Even when they didn’t know that the second thing was going to get loose, they’d outfitted it with a powerful incendiary explosive device.”

“Ah!” Alex said. “I get it! You figure they knew it was going to go off the rails eventually, so they wired it to blow if it got out of hand.”

In the depths of space, a construction welder streaked across the hull of the half-built ship, the light of its flare casting a sudden, sharp light across the pilot’s eager face.

“Yes,” Prax said. “But it could be also be an ancillary weapon, or a payload that the thing was supposed to deliver. I think it’s a fail-safe. It probably is, but it could be any number of other things.”

“Okay, but it left it behind,” Alex said.

“Given time, it ejected the bomb,” Prax said. “You see? It chose to reconfigure itself to remove the payload. It didn’t place it to destroy the Roci, even though it could have. It didn’t deliver it to a preset target. It just decided to pop it loose.”

“And it knew to do that—”

“It’s smart enough to recognize threat,” Prax said. “I don’t know the mechanism yet. It could be cognitive or networked or some kind of modified immune response.”

“Okay, Prax. So if the protomolecule can eventually get out of whatever constraints they’re putting on it and go rogue, where does that get us?” Naomi asked.

Square one, Prax thought, and launched in on the information he’d intended to give them in the first place.

“It means that wherever the main lab is—the place they didn’t release one of those things on—it has to be close enough to Ganymede to get it there before it slipped its leash. I don’t know how long that is, and I’m betting they don’t either. So closer is better.”

“A Jovian moon or a secret station,” Holden said.

“You can’t have a secret station in the Jovian system,” Alex said. “There’s too much traffic. Someone’d see something. Shit, it’s where most of the extrasolar astronomy was going on until we got out to Uranus. Put something close, the observatories are gonna get pissed because it’s stinking up their pictures, right?”

Naomi tapped her fingers against the tabletop, the sound like the ticking of condensate falling inside sheet metal vents.

“Well, the obvious choice is Europa,” she said.

“It’s Io,” Prax said, impatience slipping into his voice. “I used some of the money to get a tariff search on the kinds of arylamines and nitroarenes that you use for mutagentic research.” He paused. “It’s all right that I did that, isn’t it? Spent the money?”

“That’s what it’s there for,” Holden said.

“Okay, so mutagens that only start functioning after you activate them are very tightly controlled, since you can use them for bioweapons research, but if you’re trying to work with that kind of biological cascade and constraint systems, you’d need them. Most of the supplies went to Ganymede, but there was a steady stream to Europa too. And when I looked at that, I couldn’t find a final receiver listed. Because they shipped back out of Europa about two hours after they landed.”

“Bound for Io,” Holden said.

“It didn’t list a location, but the shipping containers for them have to follow Earth and Mars safety specifications. Very expensive. And the shipping containers for the Europa shipment were returned to the manufacturer for credit on a transport bound from Io.”

Prax took a breath. It had been like pulling teeth, but he was pretty sure he’d made all the points he needed to for the evidence to be, if not conclusive, at least powerfully suggestive.