“And you had to drag poor Matty into it,” Old Faithful said. “Matty thinks he has to please people or they’ll start hating him, just because his mum and dad did. Pretty sad, mate. And you took advantage, Nicola, so what does that make you? A bitch, right? Maybe it should be you who gets left behind.”

Walden said, in her most quelling voice, “That’s enough nonsense, thank you.”

“Oooooo,” said the demon. “Yes, miss.” It laughed. The laugh was easy and carefree, a schoolboy’s laugh.

“I know what you want,” Walden said.

“Yeah, I think I’ve been pretty clear,” said Old Faithful. “Lunch.” It slipped off the table and picked up Walden’s enamelled owl brooch. “I remember this. Wasn’t it your gran’s? Want it back?”

“I know what you want,” Walden said again. “And I know your power. If you really intended to consume my students, you could have done it an hour ago.”

The demon glanced up. In its eyes she saw a sharp, interested hunger. “Yeah?” it said. “But I didn’t, did I, Saffy? They’re only kids. Maybe I’m just nice. Maybe there’s something left in here that isn’t all demon. Did you think of that?”

Yes, Walden had thought of that. She had thought of it at once, and known it for pitiable wishful thinking. The demon smirked at her expression.

“Let’s make a deal,” Walden said. Deals with demons were her business. “First, you let both of them go.”

“Oh, I do, do I?” said Old Faithful. “What about my lunch?”

“You kept them alive this long,” Walden said. “They were never what you wanted. A pair of half-trained teenagers is barely even a light snack, for you.”

“Yeah?” said Old Faithful. Its voice had dropped to an eager whisper. “You know me so well, Saffy, huh? What’s my big plan, then?”

“The most powerful magician to step into your hunting grounds this century,” Walden said. “Me.”

She heard Mathias gasp. Old Faithful faked an unimpressed look, but she had its full attention, that was clear. “Sounds pretty noble!” it said. “The whole self-sacrifice! Making up for last time? Remember last time?”

Doubts, desires, insecurities: Walden shoved them away. Saffy, Saffy, the demon kept saying, but she was Dr Walden. She wore her adulthood like armour. “I have no intention of sacrificing anything,” she said. “Let me make my terms clear. We both know that I could easily force my way past you right now, taking one and possibly both of my pupils with me. I would then be out of your reach. My offer is this: if you let both of them go now, guaranteeing their safety by solemn oath, then I will stay here and fight you. If you win, you win. Lunch, as you say. If I win”—she paused—“I will kill you.”