Walden gave them back their homework. Will immediately tried to negotiate his mark upwards. “Check your work next time,” Walden advised. Aneeta and Nikki swapped problem sheets to look at each other’s answers to the tricky question at the end, which neither of them had quite solved, though both had got close. “Oh,” said Nikki after a moment. “It’s a substitution.” Walden nodded approval.

Mathias folded his crumpled worksheet in half and shoved it deep into a pocket.

“All right, Upper Six,” said Walden, “remind me what we’re doing today.”

“Shouldn’t you know, Doc?” said Will. “Don’t they pay you for this?”

Walden took a seat on the teacher’s desk—the four sixth formers were in their usual semicircle on the floor—and said crisply, “Thank you for volunteering, Will, take us through it, please.”

Will pantomimed stab-to-the-heart betrayal, but he did it. “Major summoning, fourth level. Uh, contain, invoke, reify, query, dismiss.”

“Good,” said Walden. “Off you go, then.”

They all stared at her.

“What?”

“Aren’t you going to tell us what to do?” said Mathias.

“I’ve spent a year and a bit telling you what to do,” said Walden. “I hope you were paying attention. Come on.” She picked up her mark book. They all looked at it with distrust. “I’ll be taking notes,” said Walden. “Oh, and Marshal Kenning should be joining us at some point. Don’t mind her, just carry on as usual.”

The sixth formers exchanged looks and mutters. It was all very well to say ‘Don’t mind her.’ They were seventeen, not stupid. They knew what Marshals were for.

“All right,” said Nikki, getting to her feet. “Let’s do it.”

“Are we allowed to work together?” said Aneeta.

Walden crossed her legs and propped her mark book on her lap. She flipped to a blank page and held the pen poised.

“She’d say if we weren’t,” pointed out Will.

Who’s she, the cat’s mother? Walden thought. Wearing her teacher outfits always made her own mental voice start to sound a bit like her grandmother. She took a note. Since she had nothing important to record yet, she wrote down what time it was.

Aneeta read it upside down. “We’re being timed!”

“I didn’t say that,” Walden said. “You have the whole double.”

“So … summoning circle, right? Salt, chalk,” said Will. “Let’s go.” He fetched supplies from the cupboard in the corner of the classroom, along with a metre ruler. “Big and central.” He got on his knees and started work on the pentagram.

“Shouldn’t we check the perimeter wards first?” said Aneeta.

“It’s a school lab, they’re fine,” Will said.

Walden said nothing.

Nikki said, “Aneeta’s right. Safety check first. Oi.” She scuffed her black school shoe across the chalk lines Will had drawn.

“Seriously?” said Will.

“North, south, east, west, windows, door, fire exit,” said Nikki. “Matty, you take this half of the room, I’ll do that half.”