"Yeah, but I mean..." She frowns. "What makes it leave? We convincing it or kicking it out? I skipped that bit of Sunday school."

But his question dredges up a memory of the creature's twisted mind, and she flinches from nothing, reacting to half remembered images. Burning pyres, snow and prayer, sacrifice... She squares down, forcing herself to think. It's all she can do, and she's stubborn and determined to win.

"I'll tell you," she says, "but you gotta promise me something first."