“Go on,” Belial said. “I’m listening.”

“I know that the things you offer us aren’t real,” Sister Emilia said. “But perhaps the illusion of a thing that we can’t have is better than nothing at all. I want you to give Brother Zachariah a vision. A few hours with the one he misses most.”

“He loves the warlock girl,” Belial said. “I could give her to him.”

“No!” Sister Emilia said. “Warlocks endure. I believe one day he will have his hours with Tessa Herondale even if he does not dare to hope for it. But his parabatai, Will Herondale, is old and frail and drawing near the end of his life. I want you to give them both a span of time. Both of them in a time and place where they can be young and happy and together.”

“And what will you give me in return?” Belial said.

“If I had agreed to your previous offer,” Sister Emilia said, “I think that my name would have lived on in infamy. And even if I was one day celebrated for my work, still every blade that I made would have been tainted by the idea that you had had some part in my successes. Every victory would have been poisoned.”

“You’re not as stupid as most Shadowhunters,” Belial said.

“Oh, stop trying to flatter me!” Sister Emilia said. “You’re wearing a suit made of human skin. No one of any sense should care what you have to say. But you should care very much about what I say to you. And that is this. I promise you if you do not give Brother Zachariah and Will Herondale the thing that I am asking for them, my life’s work will be to forge a blade that is capable of killing you. And I will go on making blades until one day I accomplish my goal. And I warn you, I am not only talented, I am single-minded. Feel free to ask my mother if you don’t believe me.”

Belial met her gaze. He blinked twice and then looked away. Sister Emilia could see, now, the way he saw her reflected in the remaining mirrors, and she quite liked, for once, how she looked.

“You are interesting,” he said. “As Brother Zachariah said. But perhaps you are also dangerous. You’re too small to make a suit. But a hat. You would make a fine trilby. And perhaps a pair of spats. Why shouldn’t I kill you now?”

Sister Emilia stuck her chin out. She said, “Because you are bored. You are curious whether or not I will be good at my work. And if my swords fail those who wield them, you will find it good entertainment.”

Belial said, “True. I will.”

Emilia said, “Then our deal?”

“Done,” Belial said. And was gone, leaving Sister Emilia in a room walled in mirrors, holding an adamas mask in one hand and in her other a sword that was quite remarkable and yet in no way the equal of the blades that she would make one day.