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.”

The split ended up being one-third to two-thirds, because Nikki was a lot faster at spellreading. But Mathias was responsible for the fire exit which Walden had altered. She took care not to watch him any more than the others. Mathias was exquisitely sensitive to the attention of authority figures. He would notice, and panic.

“Done? Can we actually get on with this now?” said Will.

“This doesn’t look right,” Mathias mumbled.

“It’s a school lab, it’s fine.”

“It doesn’t.”

“What’s wrong with it?”

“I dunno,” Mathias said. As usual, his instinct for magic was outstripping his grasp on theory. Reading the logic of someone else’s spell was not always easy, but they’d spent a long time on incursion wards last summer. Walden bit her tongue. Normally, she would have encouraged Mathias to at least try before he gave up; but the point of this exercise was to let the class figure things out by themselves.

Aneeta came and peered up at the ward next to Mathias. After a moment she gave a little screech. “Nikki!”

“What?” Nikki had moved on to ostentatiously checking on the fire extinguishers.

“Again, guys, school lab, school ward—” said Will.

“Oh shit,” said Nikki, staring at the streaks of black and yellow paint.

Will paused.

“Language,” said Aneeta, with a glance in Walden’s direction.

“Actually,” said Walden serenely, “‘Oh shit’ is the correct reaction to finding an error in an incursion ward.”

Will finally joined the other three, clustered around the fire exit. He frowned. “Is it—”

“It’s the location,” said Nikki. “It’s too vague.”

“‘This place,’” Will read, translating the loops and swirls of arcane notation on the wall.

“Could mean anything,” said Nikki. “This room, this building, this school, this whole country— Nice one, Matty.”