More common was a demon possessing an animal—it could happen randomly, if an opportunistic demon found a weakness in the fabric of reality and a living creature about the right size on the other side, and it was also the source of the old cliché about magicians summoning familiar spirits into black cats. Of course, that sort of thing was frowned on these days as being rather unfair to the cat. Technology, complex and intricate, was always a risk; hence Walden’s clock—hard to find a magician’s clock that hadn’t been possessed at some point—and the school’s draconian, much-protested mobile phone policy. Impossible to detach several hundred teenagers from their phones altogether—and their parents would have been appalled if the school had tried—but, actually, a middle schooler didn’t need a little demon box in their pocket at all times. No, they didn’t. No, turn it off. Yes, it does have to go in the dormitory safe overnight. The commonest incident reports that came across Walden’s desk were repetitive to the point of grim comedy: twelve-year-old with a secret second phone hidden under their mattress, awake at one in the morning scrolling through a social media app they were not legally old enough to sign up for, and shocked, shocked, when the imp possessing their phone started trying to eat them.

So modern technology was one risk. But actually, if anyone had ever looked at something and called it ‘you’—assigning it a self, whether it deserved one or not—then a space had been made, and in that space something could live. Provided, of course, that there was enough magic around for the demon to make the crossing from its own plane to this one.

Since Chetwood was lousy with six and a half centuries’ worth of adolescent wild magic, and the staffroom photocopier was called variations on ‘you bloody bastard thing’ by dozens of people every day, there was no point trying to keep it clear. You just ended up re-exorcising it once a week. Even the Marshals had given up. Its current inhabitant was a known quantity, and there was a large bowl of salt next to the fire extinguisher in the staffroom, in case of emergencies.

“Who told you what a strike is?” Walden asked the photocopier.

“Probably my fault,” said Marie. “We’re doing labour movements with Year Nine.”