“I can go no further,” Merringham said when they reached the door. Walden was startled again by his blurred and distant voice, by his accent with the clipped consonants of long-ago BBC announcers. “I rather think I must have failed. Did I fail?”

Walden looked at the ghost, academic gown and bad suit, gold-rimmed spectacles and greying hair. The plaque in the school chapel and the painting in the hall were all that remained in the world of this man. He had left so slight a mark on history that she doubted he even had a Wikipedia page. His brow was furrowed, his mouth anxious and sad.

And what more will remain of me, she thought, when this is all over?

A photo, rather than an oil painting. The visiting photographer had been in a hurry at the end of a long day slogging through all Year Seven. The image on Walden’s staff ID wasn’t even a nice picture.

One thing you learned, as a teacher: it was very seldom helpful, or kind, to lie to a person about themselves. They usually knew you were lying. It never made them feel better.

“I’m afraid you did fail, Mr Merringham,” she said.

“I had the most rotten teachers, as a boy,” said Merringham. “I wanted to be a good teacher, that’s all.”

“You were,” Walden said, feeling it was true, though she could not know. She had never seen him in a classroom.

“It seemed like the least I could do,” said the ghost. “We can’t have it threatening our boys.”

The incursion ward shone brightly on the door, reversed. It was painted on the other side. Its light made it hard to read the childish plaque that said, in pink bubble letters, NICOLA’S ROOM.

“I’ll take it from here, Mr Merringham,” Walden said. “Thank you for your help.”

The ghost faded away. The outline of its body became part of the shapes and shadows of the landing. Walden stood at the top of the stairs in the present-day School House’s tower. She had not been back here in twenty years. Opposite the door with Nikki’s name and the incursion ward, another door hung open, revealing through a thin layer of magical fog the detritus of teenage boy—scattered hoodies, forgotten plates, a gaming console. No sign of Mathias himself.

Walden found herself praying—oh God oh God please—as she tried the door of Nikki’s room. No atheists in foxholes.

The door would not open.