But Will never found out what Sophie was, because Thomas’s grip went suddenly slack, and his hand fell away and struck the stone floor with an ugly thump. Will drew back. He had seen death enough times, and knew when it had come. There was no need to close Thomas’s eyes; they were closed already. “Sleep, then,” he said, not quite knowing where the words came from, “good and faithful servant of the Nephilim. And thank you.”

It wasn’t enough, not nearly enough, but it was all there was. Will scrambled to his feet and dashed up the staircase.

* * *

The doors had closed behind the clockwork creatures; the Sanctuary was very silent. Tessa could hear the water splashing in the fountain behind her.

Mortmain stood regarding her calmly. He still wasn’t frightening to look at, Tessa thought. A small, ordinary man, with dark hair going gray at his temples, and those odd light eyes. “Miss Gray,” he said, “I had hoped our first time alone together would be a more pleasant experience for us both.”

Tessa’s eyes burned. She said, “What are you? A warlock?”

His smile was swift, and without feeling. “Merely a human being, Miss Gray.”

“But you did magic,” she said. “You spoke in Will’s voice—”

“Anyone can learn to imitate voices, with the proper training,” he said. “A simple trick, like sleight of hand. No one ever expects them. Certainly not Shadowhunters. They believe humans are good at nothing, as well as being good for nothing.”

“No,” Tessa whispered. “They don’t think that.”

His mouth twisted. “How quickly you have grown to love them, your natural enemies. We will soon train you out of that.” He moved forward, and Tessa shrank back. “I will not hurt you,” he said. “I merely want to show you something.” He reached into the pocket of his coat and drew out a gold watch, very fine-looking, on a thick gold chain.

Is he wondering what time it is? The mad urge to giggle rose up in the back of Tessa’s throat. She forced it down.

He held the watch out to her. “Miss Gray,” he said, “please take this.”

She stared at him. “I don’t want it.”

He moved toward her again. Tessa retreated until the back of her skirts brushed the low wall of the fountain. “Take the watch, Miss Gray.”

Tessa shook her head.

“Take it,” he said. “Or I will recall my clockwork servants and have them crush the throats of your two friends until they are dead. I need only go to the door and call to them. It is your choice.”

Bile rose in the back of Tessa’s throat. She stared at the watch he held out to her, dangling on its gold chain. It was clearly unwound. The hands had long ago stopped spinning, the time seemingly frozen at midnight. The initials J. T. S. were carved on the back in elegant script.

“Why?” she whispered. “Why do you want me to take it?”

“Because I want you to Change,” Mortmain said.

Tessa’s head jerked up. She stared at him incredulously. “What?”

“This watch used to belong to someone,” he said. “Someone I very much want to meet again.” His voice was even, but there was a sort of undercurrent beneath it, an eager hunger that terrified Tessa more than any rage might have. “I know the Dark Sisters taught you. I know you know your power. You are the only one in the world who can do what you do. I know this because I made you.”

“You made me?” Tessa stared. “You’re not saying—you can’t be my father—”

“Your father?” Mortmain laughed shortly. “I am a human, not a Downworlder. There is no demon in me, nor do I consort with demons. There is no blood shared between the two of us, Miss Gray. And yet if it were not for me, you would not exist.”

“I don’t understand,” Tessa whispered.

“You don’t need to understand.” Mortmain’s temper was visibly fraying. “You need to do as I tell you. And I am telling you to Change. Now.”

It was like standing in front of the Dark Sisters again, frightened and alert, her heart pounding, being told to access a part of herself that terrified her. Being told to lose herself in that darkness, that nothingness between self and other. Perhaps it would be easy to do as he told her—to reach out and take the watch as commanded, to abandon herself in someone else’s skin as she had done before, with no will or choice of her own.

She looked down, away from Mortmain’s searing gaze, and saw something glittering on the fountain wall just behind her. A splash of water, she thought for a moment—but no. It was something else. She spoke then, almost without meaning to.

“No,” she said.

Mortmain’s eyes narrowed. “What was that?”

“I said no.” Tessa felt as if she were outside herself somehow, watching herself face down Mortmain as if she were watching a stranger. “I won’t do it. Not unless you tell me what you mean when you say you made me. Why am I like this? Why is it that you need my power so badly? What do you plan to force me to do for you? You are doing more than just building an army of monsters. I can see that. I’m not a fool like my brother.”

Mortmain slid the watch back into his pocket. His face was an ugly mask of rage. “No,” he said. “You are not a fool like your brother. He is a fool and a coward. You are a fool who has some courage. Though it will do you little good. And it is your friends who will suffer for it. While you watch.” He turned on his heel then and strode toward the door.

Tessa bent down and seized up the object that had glittered behind her. It was the knife Jessamine had put there, the blade gleaming in the Sanctuary witchlight. “Stop,” she cried. “Mr. Mortmain. Stop.”

He turned then, and saw her holding the knife. A look of disgusted amusement spread across his face. “Really, Miss Gray,” he said. “Do you honestly think you can harm me with that? Did you think I came entirely unarmed?” He moved his jacket aside slightly, and she saw the butt of a pistol, gleaming at his belt.

“No,” she said. “No, I don’t think I can hurt you.” She turned the knife around then, so that the hilt was away from her, the blade pointing directly at her own chest. “But if you take one more step toward that door, I promise you, I’ll put this knife through my heart.”

Repairing the mess Will had made of the carriage harnesses took Jem longer than he would have liked, and the moon was worryingly high in the sky by the time he rattled through the gates of the Institute and pulled Xanthos up at the foot of the steps.

Balios, untethered, was standing by the newel post at the foot of the stairs, looking exhausted. Will must have ridden like the devil, Jem thought, but at least he had arrived safely. It was a small bit of reassurance, considering that the doors of the Institute stood wide, sending a dart of horror through him. It was a sight that seemed so wrong that it was like looking at a face missing eyes or a sky with no stars. It was something that simply should not be.

Jem raised his voice. “Will?” he called. “Will, can you hear me?” When there was no answer, he leaped down from the driver’s seat of the carriage and reached up to pull his jade-headed cane down after him. He held it lightly, balancing the weight. His wrists had begun to ache, which concerned him. Usually withdrawal from the demon powder began as pain in his joints, a dull ache that spread slowly until his whole body burned like fire. But he could not afford that pain now. There was Will to think about, and Tessa. He could not rid himself of the image of her on the steps, looking down at him as he spoke the ancient words. She had looked so worried, and the thought that she might have been worried about him had given him an unexpected pleasure.

He turned to start up the steps, and paused. Someone was already coming down them. More than one person—a crowd. They were backlit by the light of the Institute, and for a moment he blinked at them, seeing only silhouettes. A few seemed strangely misshapen.

“Jem!” The voice was high, desperate. Familiar.

Jessamine.

Galvanized, Jem darted up the stairs, and then paused. In front of him stood Nathaniel Gray, his clothes torn and spotted with blood. A makeshift bandage was wound around his head and was soaked with blood by his right temple. His expression was grim.

On either side of him moved clockwork automatons, like obedient servants. One flanked his right side, one his left. Behind were two more. One held a struggling Jessamine; the other a limp, half-insensible Sophie.

“Jem!” Jessamine shrieked. “Nate’s a liar. He was helping Mortmain all this time—Mortmain’s the Magister, not de Quincey—”

Nathaniel whirled. “Silence her,” he barked at the clockwork creature behind him. Its metal arms tightened around Jessamine, who choked and fell silent, her face white with pain. Her eyes darted toward the automaton on Nathaniel’s right. Following her gaze, Jem saw that the creature held the familiar golden square of the Pyxis in its hands.

At the look on his face, Nate smiled. “None but a Shadowhunter can touch it,” he said. “No living creature, that is. But an automaton is not alive.”

“That is what all this was about?” Jem demanded, astounded. “The Pyxis? What possible use could it be to you?”

“My master wants demon energies, and demon energies he shall have,” said Nate pompously. “Nor will he forget that I am the one who provided them for him.”

Jem shook his head. “And what will he give you then? What did he give you to betray your sister? Thirty pieces of silver?”

Nate’s face twisted, and for a moment Jem thought he could see through the blandly handsome mask to what was really underneath—something malignant and repellent that made Jem want to turn away and retch. “That thing,” he said, “is not my sister.”

“It is hard to believe, isn’t it,” said Jem, making no effort to hide his loathing, “that you and Tessa share anything at all, even a single drop of blood. She is so much finer than you.”

Nathaniel’s eyes narrowed. “She is not my concern. She belongs to Mortmain.”

“I don’t know what Mortmain has promised you,” Jem said, “but I can promise you that if you hurt Jessamine or Sophie—and if you take the Pyxis from these premises—the Clave will hunt you. And find you. And kill you.”

Nathaniel shook his head slowly. “You don’t understand,” he said. “None of the Nephilim understand. The most you can offer is to let me live. But the Magister can promise me that I won’t ever die.” He turned to the clockwork creature on his left, the one not holding the Pyxis. “Kill him,” he said.

The automaton sprang toward Jem. It was faster by far than the creatures Jem had faced on Blackfriars Bridge. He barely had time to flip the catch that released the blade at the end of his cane and raise it, before the thing was on him. The creature squealed like a braking train when Jem drove the blade directly into its chest and sawed it from side to side, tearing the metal wide open. The creature spun away, spraying a Catherine wheel of red sparks.