Outside Lab Three, uncharacteristically early and flicking brazenly through his phone as if he’d never heard of a personal electronics policy, was one of her Upper Sixth. He’d arranged himself, his school rucksack, a rainbow collection of lever arch folders, and a hefty bag of sports kit all in an array on the floor, in such a way as to present a tripping hazard to unwary passersby. “Will,” said Walden. “Legs.”

“Sorry, miss,” said Will, and drew his long legs in black jeans—not the smart trousers mandated by the sixth form dress code—up into a tightly acute triangle, which improved the situation only slightly.

“Will.”

Will looked up from his phone and bestowed upon Walden his most winning smile. “Sorry, Doc,” he said.

“William Daubery, clear this corridor right now or face my wrath,” said Walden. “I ought to dress code you and PEP you.” School rules inevitably turned into verbs. To dress code: to send a child back to their dormitory to change. To PEP: to confiscate a misused mobile phone. The personal electronics policy was relaxed a little for sixth formers, but Will, who was more than halfway through A-levels in Invocation, Evocation, and Further Evocation, ought to know better than to play with a tasty little electronic device right outside the arcane labs. Yes, the risk was low, because Walden ran a tight ship. But part of keeping the arcane labs magically secure was knowing that ‘low’ and ‘nonexistent’ were very different beasts.

“Whoops,” said Will, but he obediently got up and hefted his possessions over to the wall, and the phone—a large and expensive-looking model, he would no doubt be very annoyed if it did get possessed and had to be destroyed—went into the front pocket of his rucksack. “Haven’t you had your coffee yet, Doc?”

“No, I haven’t,” said Walden sternly. “And so I’m in a very bad mood. Don’t test me.”

Will faked a shudder. “I’ll warn the others.”

“See that you do,” Walden said. “And turn your phone off in the arcane corridor, and don’t spread your things all over the floor again. Someone will trip and break a leg. Remember, I have eyes in the back of my head.”

“Yes, miss. Doc!”

Walden unlocked Lab Three and let herself in. There was just time before the bell to finish her lesson prep and gulp down about half the black-sludge coffee. She plucked the risk assessment out of her pile of papers and slapped it down front and centre on the big desk at the front of the room.