Before that line of conversation could be pursued, the dark-hooded necromancer of the Ninth said in her most sepulchrous and forbidding tones: “We have business down here, Lady Septimus. Excuse us.”

“But that’s just what I came to talk to you about,” said the other necromancer earnestly. “I think we four should team up.”

Gideon could not hide an explosive snort of disbelief. There were maybe less likely targets for Harrow to team up with—Silas Octakiseron, maybe, or Teacher, or the dead body of Magnus Quinn. In fact, Teacher would be a far better candidate. But Dulcinea’s dreamy blue eyes were turned on Harrow, and she said:

“I’ve already completed one of the theorem labs. I think I’m on the path to cracking another. If we both worked together—why, then, there’s the key in half the time with just a few hours’ work.”

“This is not intended to be collaborative.”

Dulcinea said, smilingly: “Why does everybody think that?”

The women sized each other up. Dulcinea, leaning into her metal braces, looked like a brittle doll: Harrow, hooded and swathed in miles of black fabric, like a wraith. When she pulled away the hood the older necromancer did not flinch, even though it was a deliberately chilling sight; the dark-cropped head, the stark paint on the face, the bone studs punched halfway up each ear. Harrow said coolly: “What would be in it for the Ninth House?”

“All my knowledge of the theory and the demonstration—and first use of the key,” said Dulcinea, eagerly.

“Generous. What would be in it for the Seventh?”

“The key once you’re done. You see, I don’t think I can physically do this one.”

“Stupidity, then, not generosity. You just told me you can’t complete it. Nothing would stop my House from completing it without you.”

“It took me a long time to work out the theoretical parameters,” said Dulcinea, “so I wish you the best of luck. Because even though I’m dying—there’s nothing wrong with my brain.”

Harrow pulled the hood back over her head, returning her to a wraith, a piece of smoke. She swept past the frail necromancer of the Seventh, who followed her with the wistful, somewhat hungry expression that Dulcinea reserved for the shadowy nuns of the Ninth—for the black robes whispering on the metal floor, the green light reflecting off dark fabric.

Harrowhark turned around and said, curtly: “Well? Are we doing this or not, Lady Septimus?”

“Oh, thank you—thank you,” Dulcinea said.

Gideon was stupefied. Too many shocks in twenty-four hours shut down her thought processes. As Dulcinea stumped along the corridor, crutches clanging unharmoniously on the grille, and as Protesilaus hovered behind her a half step away as though desperate to just scoop her up and carry her, Gideon strode to catch up with her necromancer.

Only to find her swearing under her breath. Harrow whispered a lot of fuck-words before muttering: “Thank God we got to her first.”

“I never thought you’d actually help out,” said Gideon, grudgingly admiring.

“Are you dim,” hissed Harrow. “If we didn’t agree, that bleeding heart Sextus would, and he’d have the key.”

“Oh, whoops, my bad,” said Gideon. “For a moment I thought you weren’t a huge bitch.”

They followed the mismatched pair from the Seventh House to the dusty facility hub, filled with its dusty panelling and its whiteboard gleaming sadly beneath big white lights. Dulcinea turned abruptly down the passageway marked LABORATORY SEVEN–TEN, a tunnel identical to the one they had taken to LABORATORY ONE–THREE. This time the creaks and ancient moans of the building seemed very loud, their footsteps a huge addition to the cacophony.

In the middle of a passage past the first laboratory rooms the grille on the floor had been staved in, cracked right down the middle to come to rest on hissing pipes. Protesilaus picked up his adept and stepped her over this pit as lightly as thistledown. Gideon jumped the gap, and turned back to see her necromancer hesitating on the edge, stranded. Why she did it Gideon didn’t know—Harrow could have built herself a bridge of bones any second—but she grasped a railing, leaned over, and proffered her hand. Why Harrow took it was an even bigger mystery. After being helped across, Harrow spent a few moments officiously dusting herself off and muttering inarticulately. Then she strode off to catch up with—of all people—Protesilaus, apparently with the aim of engaging him in conversation. Dulcinea, who had taken a moment to fit herself back into her crutches, slipped one arm into Gideon’s instead. She nodded at the broad span of her cavalier’s back.

“Colum the Eighth is fixing to fight him tomorrow,” she said to Gideon, beneath her breath. “I wish Master Silas had just fought me. Not much can hurt me anymore … it would be an interesting sensation, is what I mean.”

In response Gideon’s grip tightened around the languid arm tucked in her own. Dulcinea sighed, which sounded like air being pushed through whistly sponges. (Up this close her hair was very soft, Gideon noted dimly.) “I know. I was an idiot to let it happen. But the Eighth are so touchy in their own way … and Pro was unpardonably bad. They couldn’t let the insult pass. I just let my worst instincts get the better of me … and yelped.”

The curly-haired necromancer paused to cough, as though simply remembering how she’d yelped was enough to send her into spasms. Gideon instinctively put an arm around her shoulders, steadying her so that the crutches did not give way, and found herself looking down where the edge of Dulcinea’s shirt met her bulging collarbones. A fine chain around her neck supported a rather less delicate bundle hanging tucked into her camisole: Gideon only saw them for a second, but she knew immediately what they were. The key ring was snapped around the chain, and on the key ring were two keys: the saw-toothed hatch key, and a thick grey key with unpretentious teeth, the kind you’d lock a cabinet with.

She made herself look anywhere else. By now they had reached the very end of the corridor, which terminated in a single door marked LABORATORY EIGHT. Wriggling free of Gideon’s arm, Dulcinea opened it onto a little foyer alike in indignity to LABORATORY TWO. There were hooks on the walls here, and a bunch of old, crumpled boxes made of thin metal, the type you might carry files in; these were dented and empty. Someone had taken the time and effort to affix a beautiful swirl of human teeth above the door in a widening spiral of size: in the centre, the neat little shovels of incisors, tessellated with arched canines and ringed all around with the long, racine tusks of molars. In neat print the label on the door read: #14–8 DIVERSION. PROCEDURAL CHAMBER.

Beneath the neat print, a more elaborate hand had written in fainter ink: AVULSION!

“Here we are,” said Dulcinea. “Before we go through, please give me a little bit of your blood. I have warded the place up and down and I’m dreadfully afraid you won’t be able to go through the door without giving me a shock.”

This little nod to paranoia made Harrow’s shoulders relax minutely. Gideon looked to her, and Harrowhark nodded. In the dim and dusty foyer both offered up their hands to be pricked: the necromancer of the Seventh tilted her head, beautiful brown ringlets spilling over her shoulders, and took blood from their thumbs and their ring fingers. Then she pressed the blood into her palm and spat delicately with what Gideon noticed was pink-tinged spittle; she pressed her thin hand to the door.