The lab was otherwise almost empty. The science labs, on the other side of the building, were fully equipped with sinks and Bunsen burners and fume cupboards and all the other apparatus of a twenty-first-century scientific education. Modernity had taken magic in the other direction. The arcane labs were stripped down as far as possible; the less there was in here, the less possibility that someone would accidentally start you-ing something and invite in an unwelcome demon. The room was painted white floor to ceiling, and had no desks except the teacher’s and no chairs at all. There was a whiteboard on the wall behind the desk; the pens were kept in a jar of salt, because Walden knew from bitter experience how easy it was to accidentally say Where are you? to a missing board pen.

When she taught magical theory, she booked one of the seminar rooms upstairs, so her class wouldn’t have to work on the floor. But for practical work, the arcane lab was a necessity.

Very stark in black and yellow against the white safety paint were the incursion wards: north, south, east, west, one over the door, one over the fire exit, one for each of the windows. They were repainted every half term. Walden checked them for errors, fading, or alerts, as she did before every lesson. Then, slowly and with great care, she introduced a minor location error into the ward above the fire exit, changing its area of effect from ‘this laboratory’ to ‘this place.’ It took her almost to the bell, with two minutes to spare. She swallowed another bitter gulp of coffee.

She shuffled through her papers for Upper Sixth’s homework—four problem sheets on arcane attribution, handed in last week and marked yesterday evening. The work was about what she’d expected: Nikki outstanding, Will slapdash, Aneeta careful, Mathias skipping questions that worried him. Walden put them to one side. She paused to straighten her shoulders and arrange her face, putting aside her late night and Laura Kenning and the photocopier demon, putting on—like the armour of blazer and skirt and brooch—the total good-humoured calm of Dr Walden, teacher.

The bell went.

“Come in!” Dr Walden called.

And in they came, shambling, sauntering, seventeen years old: Upper Sixth Invocation.

Walden did not do much frontline teaching anymore. Director of Magic was a deputy-head-level role, and the further you climbed the ladder of a career in education, the less you got to actually teach. Her work calendar was full of meetings, conferences, presentations, project deadlines. There was blocked-out time for boundary patrols and spot checks, and apparently free time which always filled up immediately with crisis management: constant variations on the stern talking-to for the middle schooler with the secret phone under the mattress, along with the diplomatic but firm talking-to for the loving parent who had purchased the phone.