No. Multiple things had failed. There were backups to the backups. There was a whole additional layer of alerts that she’d spent a month installing two summers ago. She’d been doing planar patrols weekly since last November, and so had Mark Daubery. The Marshals had been on high alert ever since Old Faithful’s incursion had made them all look like fools. Todd as Keymaster walked the mundane boundaries of the entire site every couple of days. And still something had slipped by all of them. David’s expression grew graver and graver as she laid it all out. Magic was her responsibility; but Chetwood, all of it, the whole school, was his responsibility. If she could not find the hole in the school’s defences, and fix it, and explain how and why it could possibly have happened in the first place, she would be out of a job by the end of term. David’s slightly more graceful resignation would follow by the end of the academic year.

They would both deserve it. The first responsibility of any school was to keep the children safe.

“Where’s the problem?” David asked sharply once he’d grasped the situation, as if that wasn’t the exact question that Walden was going to lose sleep over tonight.

“It could be anywhere,” she said. “Anywhere at all. We’ll have to go over the whole site.”

“For my money it’s those old engines,” said Todd. “If it’s anywhere it’s there. Apologies, Mr Bern, Dr Walden—just an old man’s feeling.”

“You’re probably right,” Walden said. “Which is why I’m going to start with a full check on the thaumic engines. It’s a summer holiday job, usually.”

“Did you do it last summer?” said David.

“Yes,” said Walden. She was too tired and worried to even be annoyed that he’d apparently forgotten the detailed report she submitted every September. “And they were fine. As fine as a hideous nineteenth-century bodge job can possibly be. There are hundreds of possible failure points, magical and mechanical. We’ll have to go through all of them.”

She got back to her flat after midnight. She was listening for it, so she could hear the rumble of the thaumic engines as they hummed to themselves next door. They sounded all right.

She went through her office on her way into the flat. Someone had left a pile of papers on her desk. Walden paused to look at them and discovered that they were the A-level mock papers for her set. She’d meant to mark them tomorrow. It was a good three hours of brain work. The deadline for getting the grades in the system was Monday lunchtime.

This was the job. This was school. It never stopped.

chapter twenty-four MOCKS