Walden focused fiercely on her shielding and scouting spells, and tried not to listen while Nikki talked softly to Mathias. A twitch at the edges of her perception; Old Faithful was testing how attentive she was. Walden narrowed her eyes and turned to face that way. Another twitch, now directly behind her. She turned again. She still hadn’t actually seen the demon. It was too big. Now it tugged at Walden’s spiderweb in two places at once. She had a feeling it was laughing at her.

“Dr Walden, I think we’re ready,” Nikki said. She’d got Mathias standing, and had a protective arm around him. Mathias was alarmingly pale, the scattering of his acne a livid constellation of red on his forehead and chin. He was still breathing too fast. But Nikki at least looked better, if still very tired. Walden had hoped that having someone else to look after would calm her down. It was the main reason she was calm, after all.

“All right,” Walden said. She made direct, intentional eye contact, first with Nikki and then with Mathias. “We’re all going to walk together. Stay calm and stay with me. Don’t try to hurry. Don’t attempt any magic yourselves. I’ve got you shielded and I will keep you safe. Do you understand?”

Nikki nodded. After a moment, Mathias did too.

“Good,” said Walden. “Let’s go.”

How long ago had Walden left her enamelled owl brooch jammed into the wall of School House’s kitchen? The twist of magic looped through it was a shining beacon to her now. The distorted space of the demonic plane was under Old Faithful’s control and did its best to confuse her, throwing up classrooms that no longer existed and dormitories that had long since been emptied. The great demon was pulling in spaces from the rest of the school now: a section of Brewers Hall, a space punctuated with columns from the colonnade, the shining glassy conference room walls from the new Bursary building, even a double room from Scrubs. Walden bit her lip when she noticed but said nothing. She did not want to frighten the children.

She’d left Laura Kenning outside School House, and she remembered that glimpse of a perimeter. Walden had colleagues who knew what they were doing. If the incursion started spreading quickly, then collapsing it was the only option. An incursion collapse would be experienced by everything inside it as an explosive detonation. Death would be fast, if Walden dropped her shield; or slow, eaten alive by hundreds of demons, if she tried to save herself. How far away now was her two-hour deadline? If the three of them could not find their way out in time—

No use worrying. It would be more dangerous if they tried to run.