There was a frequency scale, or something like it. Every alternate Earth could be identified by its specific resonance. The Plug-uglies made use of it, but so did the rat-creatures who had Khan. The rats and the Plug-uglies were now in some kind of cold war, and the rats were able to shield sensitive sites from intrusion by the Uglies. And I bet Hind would give a lot to duplicate that feat. It wasn’t that the Plug-uglies could just walk in and out of wherever they wanted—there were fault lines and weaknesses between worlds that they had to exploit. Yet where those faults existed, they could walk, and there wasn’t a blind thing human security forces could do to stop them. If a crack opened into Number 10 Downing Street, then the PM might find unexpected guests at the breakfast table.

Those faults, in and of themselves, were a symptom of the wider problem, of course: that the boundaries between worlds were falling. The problem the Uglies wanted Khan’s help in solving, or so they said.

Musmursumbrer had explained haltingly that the rats were not taking steps to protect themselves from intrusions by humans, because humans didn’t have the capability to intrude on their spaces. Hence the Plug-uglies needed a human-resonant task force to go get Khan, and they would provide the means.

Everyone, Hind included, had assumed this meant an MI5 team. Julian had begun making plans there and then. The Plug-ugly woman had broken in immediately, apologetically. Apparently there had been a misunderstanding. They had chosen who they were sending in already. What they needed the department’s help with was the extraction.

When the team came out with Khan, the rats would likely be in hot pursuit. The Uglies needed a rearguard, someone to take the flak. Not the most enviable part of the plan, but Alison had seen the calculations in Hind’s mind. A plan that put Khan and a concentration of human armed forces in the same place gave them the best chance of hanging on to the scientist, post-rescue.

After the briefing, Alison ended up in Julian’s office again, and he said, “I suppose we have to stop calling them Plug-uglies, now we’re working with them.”

She laughed, and it lit him up in a way she’d missed. “To their faces, certainly. I was thinking—based on what they are, what they say they are—we could call them Cousins.”

“Nice. Just the right connotation of inbreeding.” Julian shook his head. “Who the hell is on their rescue team, anyway? Who else are they working with? The Americans, you think?”