There was a Year Nine class in PE kit in Lab One. This arcane lab was one of the ones that usually belonged to the Evocation Department, and so it was less snowy and pristine than the lab Walden taught her practicals in. Just now there were soot stains down one wall and scuff marks on the white-painted floor. Two thirteen-year-olds stood facing each other in the middle of an excited, noisy semicircle of their classmates. One of them had a handful of conjured green fire; the other was trying to evoke a shield, not very successfully. Lilly’s intake of breath told Walden that this was not the position she’d left them in.

She shouldn’t have left them at all—not this age group, not unsupervised in a lab, not when she had a weird feeling already. Lilly hadn’t been able to clarify what her bad feeling was, but ‘something’s not right here’ was part of a teacher’s toolkit, not to be disregarded. School days were so extremely routine that you became sensitised to the tiny variations that signalled something out of place, and began to develop a gut instinct for which variations were the bad ones. Walden would talk to Lilly later about when to send a reliable-looking child to run your errands for you.

Under other circumstances she would have let the junior teacher handle her own class, but the moment she stepped through the lab door she felt it too. Something was not right, in a way that went beyond the obvious misbehaviour. She looked at the incipient evocation duel and snapped, “Sit down immediately, Year Nine.”