Harrow let out a cry of triumph. Gideon turned away from the beds and put the flimsy in her pocket, then stretched over the stair railing to see what her necromancer was delighted about. She was by the workbench staring at two great stone tablets that had been fused to the stone, shot through with pale green filaments glowing beneath Harrow’s touch. The writing was small and cramped and the diagrams totally impenetrable in their obtuseness. Harrow was already pulling out her journal.

“It’s the theorem from the trial room,” she called out. “It’s the completed methodology for transference—for the utilisation of a living soul. It’s the whole experiment.”

“Is this an exciting necromancer thing?”

“Yes, Nav, it is an exciting necromancer thing. I need to copy this down, I can’t lift the stone. Whoever did this was a genius—”

Gideon let Harrow have at it, and opened the first drawer of the nightstand. Sitting there, offensively ordinary, were three pencils, a finger bone, a coarse sharpening stone—bones and whetstones were beginning to feed her growing suspicion about who’d lived there—and an old, worn-down seal. She stared at the seal awhile: it was the crimson-and-white emblem of the Second House.

She sat down carefully on one of the beds, and the sprung mattress squeaked. She took the piece of crumpled-up flimsy out of her pocket and began trying to uncrumple it. It was part of a note that had—at some long-ago point—been ripped up, and this was just one scrunched corner.

“I’m done,” said Harrow, from below. “Tell me anything of import.”

Gideon stuffed the piece of flimsy back into her pocket and had a quick scan through the other drawers. A lost sock. A scalpel. Oilcloth. A tin with nothing in it but the vague waft of peppermints. This was all the stuff you’d find in anyone’s bedside drawers—though then again, not quite anyone’s; a particular pair of people. She descended the stairs and tipped her dark glasses high on her head. “A cav and their necro lived here,” she said.

“I drew the same conclusion,” said Harrowhark, shuffling her papers. She put one of her diagrams close to the one inscribed on the stone tablet to compare them for accuracy. “Here. Come and take a look at this.”

Harrow’s cramped handwriting was just as bad as the etching on the tablet. At the very end of a long list of exquisitely boring notes was a line on its own:

In the hope of attaining Lyctoral understanding. All glory and love to the Necrolord Prime.

The Ninth necromancer said, “Now there’s a helpful postscript if ever I saw one.”

“Yeah, and the fact that there are two beds upstairs and a bunch of swords also help,” said Gideon. “They were living in each other’s pockets. They studied weird Lyctoral theorems. There’s a seriously old Second House sign in one of the top drawers.”

They both took the time to roam around the room. Harrow flicked through notebooks and narrowed her eyes over the contents. Gideon picked up another book and squinted at the faded message on the flyleaf, written in black ink forever ago and frozen in time:

ONE FLESH, ONE END.

G. & P.

They combed over the detritus of two strangers’ lives; inside a forgotten tin Gideon found two expired toothbrushes. They were electronic ones, with revolving heads and push buttons.

“These aren’t just seriously old, they’re super unbelievably seriously old,” she said.

“Yes,” said Harrow. “Sextus could tell us how old, but I’ve no desire to ask him. Something has been done to preserve this room. It has not wasted away into a natural death. We’re probably the first people to step inside since its previous occupants left.”

It didn’t seem to be a proper bedroom; more like a place to stay overnight while doing something else. More lab than living space. Gideon ended up staring at the photo-lithograph, elbows pressed into the countertop, studying faceless bodies gathered primly in their chairs. A rainbow of arms and robes; low-resolution hands clasping low-resolution knees. The hands without faces seemed solemnly posed, almost anxious.

“All I know,” said Harrowhark eventually, “is that they created the theorem, and were responsible for the experiment downstairs. I wish I knew more. I yearn to know more … But I don’t. I’m going to study this spell, Griddle, and learn it, and then I will be one step closer to knowing. We cannot suffer the same fate as Quinn and Pent.”

Gideon was amazed at how badly it hurt, all of a sudden.

“He’s really dead,” she said aloud.

“Yes. I will be more upset if he suddenly changes condition,” said Harrow. “He was a stranger, Nav. Why does it affect you so much?”

“He was nice to me,” she found herself saying. She was very tired. She tried to wake herself up by stretching, dropping down to touch her toes and feeling the blood rush into her head. “Because he was a stranger, I think … He didn’t have to bother with me, to make time for me or remember my name, but he did. Hell, you treat me more like a stranger than Magnus Quinn did and I’ve known you all my life. Anyway, I don’t want to talk about it.”

Harrow’s hand, peeled and naked without a glove and stained with ink all the way up to her cuticles, appeared in front of her. Gideon found her shoulder drawn back so that she had to look Harrow square in the face. The necromancer regarded her with a strangely fierce eye: mouth a worn-down line of indecision, forehead puckered as though she was thinking her entire face into a wrinkle. There was still blood flaking out of her eyebrows, which was gross.

“I must no longer accept,” she said slowly, “being a stranger to you.”

“Whoa, whoa, whoa,” said Gideon, sudden sweat prickling the back of her neck, “yes you can, you once told me to dig myself an ice grave. Stop before this gets weird.”

“Quinn’s death proves that this is not a game,” said Harrow, moistening her ashy lips with her tongue. “The trials are meant to winnow out the wheat from the chaff, and it is going to be exceptionally dangerous. We are all the sons and daughters that the House of the Ninth possesses, Nav.”

“I’m not anybody’s son or daughter,” said Gideon firmly, now in no small panic.

“I need you to trust me.”

“I need you to be trustworthy.”

In the thick dimness of the room she watched the black-garbed girl in front of her struggle around a thing that had settled over them like a net; a thing that had fused between them like a badly broken limb, shattered numerous times, healing gnarled and awful. Gideon recognised these strictures all of a sudden: the rope tying her to Harrow and back to the bars of the House of the Ninth. They stared at each other with shared panic.

Harrow said finally, “In what way can I earn your trust?”

“Let us sleep for eight bloody hours and never talk like this again,” said Gideon, and her necromancer relaxed, very minutely. Her eyes were so lightlessly black that it was hard to see the pupil; her mouth was thin and waspish and unsure. She remembered when Harrow was nine, when she had walked in at just the wrong moment. She remembered that nine-year-old Harrow’s mouth falling slightly slack. There was something curious about Harrow’s face when it was not fixed into the bland church mask of the Reverend Daughter: something thin and desperate and quite young about it, something not totally removed from Jeannemary’s desperation.