After lunch, in the high room next door to her flat, surrounded by heavy glass panels set into walnut-and-brass facades, Walden tuned up the thaumic engines. She didn’t deal with the physical, mechanical side—that probably should have been handed off to an Instantiation teacher, but in practice none of them was as good at it as Todd Cartwright, who’d been adjusting misaligned gears and replacing damaged pneumatic tubes for the better part of forty years. Walden’s business was the invisible magical web of defences that the engines powered. She worked with salt and red chalk, drawing intricate miniaturised warding arrays on the wide parquet floor with the humming engines surrounding her—miniaturised because they were a mere fifteen feet across, rather than the several acres they needed to be to cover the whole school site. Every time she finished one, she flipped half a dozen brass switches. The engine’s hum deepened, and the latest refreshed ward flashed gold and then vanished as it got picked up and projected outwards.

Today, Walden spent longer than usual on the ward against higher demons. I belong here. You know I do, something whispered—not a true demonic whisper, just a memory sharpened by worry. It was rare for Old Faithful to stir. The old monster had been feeding on the ambient wild magic of Chetwood for centuries, and that was usually enough to keep it satisfied. It was very bad luck for a magical working as small as a sixth form lesson to attract its attention. If only Mathias wasn’t so strong!

Walden kept a close eye on Mathias in their lessons that week, but he seemed fine: shaken, but fine. Will was making a show of being friendlier and more considerate towards him than usual. Aneeta was quiet in lessons—well, she was a quiet person. Nikki, meanwhile, seemed to be enjoying the fourth-order summoning topic. She wrote notes frantically fast in their theory lesson on Thursday, and peppered Walden with questions. She really was a delight to teach. Walden had to be careful not to let herself get drawn into the weeds: several times she found herself saying That’s a bit too advanced for what we’re doing here, Nikki, but if you want to read up on it … By the end of the week she’d dug out her undergrad copy of Nielle’s Arrays, very dog-eared—Walden had once referred to it several times a day, though nowadays she had most of it by heart—and very useful. Nikki accepted it with an air of determination. “Thank you, Dr Walden,” she said.

“Nerd,” said Will across the classroom. Nikki only glanced at him, uninterested, and then started flicking through the book. Will looked disappointed not to get more of a reaction.