Harrow sighed. Then she rummaged in her pocket and took out a little nodule of bone, which she placed in the palm of her right hand. “All right,” she said. “Describe it for me.”
Palamedes stared at her.
“Hurry up,” she prompted. “I’m not waiting for the Second to find us.”
“It—I mean, it looked like a key,” he said. “It had a long shaft and some teeth. I don’t—I can’t just describe a molecular structure like it’s someone’s outfit.”
“Then how exactly am I meant to replicate it?” demanded Harrow. “I can’t—oh. No.”
“You did Imaging and Response, right? You must have, you got the key for it. Same deal. I’m going to think about the key, and you’re going to see it through my eyes.”
[...]
Palamedes closed his eyes. Harrow gnawed on her lip furiously, then closed hers too.
Nothing happened for a good thirty seconds. Gideon was dying to make a joke, just to get a reaction, when the tiny lump of matter in Harrow’s palm twitched. It flexed and began to stretch, forming a long, thin, cylindrical rod. Another few seconds passed, and a spine of bone extruded slowly from near one end. Then another.
Gideon was honestly impressed. In all the time Harrow had tormented her back on Drearburh, she had only ever used bones as seeds and starters—stitching them together into trip wires, grasping arms, kicking legs, biting skulls. This was something new. She was using bone like clay—a medium she could shape not just into one of a bunch of predetermined forms, but into something that had never existed before. It looked like it was giving her trouble too: her brow was furrowed, and the first faint traces of blood sweat gleamed on her slim throat.
“Focus, Sextus,” her necromancer gritted out. The object on her palm was now clearly a key: Gideon could see three individual teeth, twisting and flexing as Harrow filled in the fine detail. The whole length of the key quivered, and looked for a moment as though it would jump off her hand and fall to the floor, but then it abruptly lay still. Harrow opened her eyes, blinked, and peered at it suspiciously.
“This won’t work,” she said. “I’ve never had to work with something so small before.”
“That’s what she said,” murmured Gideon, sotto voce.
Palamedes opened his eyes too, and breathed a long sigh of what sounded like relief.
“It’ll be fine,” he said unconvincingly. “Come on. Let’s try it out.”
He headed for the black stone door, followed by Harrow, both cavaliers, and the five skeletons that Harrow had refused point-blank not to conjure on their way up here. He took the newly formed bone key, examined it, fitted it in the lock, and then turned it decisively to the left.
The mechanism went click.
“Oh, my God,” said Harrow.

Gideon the Ninth - Act Four, Chapter Thirty-One