Nate, caught by the spray of fire, yelled and jumped back, beating at the sparks burning holes into his clothes. Jem took the opportunity to leap up two of the steps and slam Nate across the back with the flat of his blade, knocking him to his knees. Nate twisted around to look for his clockwork protector, but it was staggering from side to side across the steps, sparks fountaining from its chest; it seemed evident that Jem had severed one of its central mechanisms. The automaton holding the Pyxis stood stock-still; clearly Nate was not its first priority.

“Drop them!” Nate cried to the clockwork creatures holding Sophie and Jessamine. “Kill the Shadowhunter! Kill him, do you hear?”

Jessamine and Sophie, released, tumbled to the ground, both gasping but clearly still alive. Jem’s relief was short-lived, though, as the second pair of automatons lurched toward him, moving with incredible speed. He slashed out at one with his cane. It leaped back, out of range, and the other raised a hand—not a hand, really, more a square block of metal, its side edged with ragged teeth like a saw—

A yell came from behind Jem, and Henry charged past him, wielding a massive broadsword. He swung it hard, slashing through the automaton’s raised arm and sending its hand flying. It skidded across the cobblestones, sparking and hissing, before bursting into flames.

“Jem!” It was Charlotte’s voice, raised in warning. Jem spun, and saw the other automaton reaching for him from behind. He drove his blade into the creature’s throat, sawing at the copper tubes inside, while Charlotte slashed at its knees with her whip. With a high whine, it collapsed to the ground, legs severed. Charlotte, her pale face set, brought the whip down again, while Jem turned to see that Henry, his ginger hair pasted to his forehead with sweat, was lowering his broadsword. The automaton he had attacked was now a heap of scrap metal on the ground.

In fact, bits of clockwork were scattered across the courtyard, some of it still burning, like a field of fallen stars. Jessamine and Sophie were clinging to each other; Jessamine supporting the other girl, whose throat was necklaced with dark bruises. Jessamine met Jem’s eyes across the steps. He thought it might have been the first time she’d really ever looked like she was glad to see him.

“He’s gone,” she said. “Nathaniel. He vanished with that creature—and the Pyxis.”

“I don’t understand.” Charlotte’s bloodied face was a mask of shock. “Tessa’s brother …”

“Everything he said to us was a lie,” said Jessamine. “The whole business with sending you off after the vampires was a diversion.”

“Dear God,” said Charlotte. “So de Quincey wasn’t lying—” She shook her head, as if to clear it of cobwebs. “When we reached his house in Chelsea, we found him there with just a few vampires, no more than six or seven—certainly not the hundred Nathaniel had warned about, and no clockwork creatures that anyone could find. Benedict slew de Quincey, but not before the vampire laughed at us for calling him the Magister—said we had let Mortmain make fools of us. Mortmain. And I’d thought he was just—just a mundane.”

Henry sank down on the top step, his broad sword clanking. “This is a disaster.”

“Will,” Charlotte said dazedly, as if in a dream. “And Tessa. Where are they?”

“Tessa’s in the Sanctuary. With Mortmain. Will—” Jessamine shook her head. “I didn’t realize he was here.”

“He’s inside,” Jem said, raising his gaze to the Institute. He remembered his poison-racked dream—the Institute in flames, a haze of smoke over London, and great clockwork creatures striding to and fro among the buildings like monstrous spiders. “He would have gone after Tessa.”

Mortmain’s face had drained of blood. “What are you doing?” he demanded, striding toward her.

Tessa set the tip of the blade to her chest and pushed. The pain was sharp, sudden. Blood bloomed on the bosom of her dress. “Don’t come any closer.”

Mortmain stopped, his face contorted with fury. “What makes you think I care if you live or die, Miss Gray?”

“As you said, you made me,” said Tessa. “For whatever reason, you desired that I exist. You valued me enough that you would not have wanted the Dark Sisters to harm me in any permanent way. Somehow, I am significant to you. Oh, not my self, of course. My power. That is what matters to you.” She could feel blood, warm and wet, trickling down her skin, but the pain was nothing compared to her satisfaction at seeing the look of fear on Mortmain’s face.

He spoke through gritted teeth. “What is it you want from me?”

“No. What is it you want from me? Tell me. Tell me why you created me. Tell me who my true parents are. Was my mother really my mother? My father, my father?”

Mortmain’s smile was twisted. “You are asking the wrong questions, Miss Gray.”

“Why am I … what I am, and Nate is only human? Why is he not like me?”

“Nathaniel is only your half brother. He is nothing more than a human being, and not a very good example of that. Do not mourn that you are not more like him.”

“Then …” Tessa paused. Her heart was racing. “My mother could not have been a demon,” she said quietly. “Or anything supernatural, because Aunt Harriet was her sister, and she was only human. So it must have been my father. My father was a demon?”

Mortmain grinned, a sudden ugly grin. “Put down the knife and I will give you your answers. Perhaps we can even summon up the thing that fathered you, if you are so desperate to meet him—or should I say ‘it’?”

“Then I am a warlock,” Tessa said. Her throat felt tight. “That is what you are saying.”

Mortmain’s pale eyes were full of scorn. “If you insist,” he said, “I suppose that is the best word for what you are.”

Tessa heard Magnus Bane’s clear voice in her head: Oh, you’re a warlock. Depend on it. And yet—

“I don’t believe any of this,” Tessa said. “My mother, she would never have—not with a demon.”

“She had no idea.” Mortmain sounded almost pitying. “No idea that she was being unfaithful to your father.”

Tessa’s stomach lurched. This was nothing she hadn’t thought might be possible, nothing she hadn’t wondered about. Still, to hear it spoken aloud was something else. “If the man I thought was my father, was not my father, and my true father was a demon,” she said, “then why am I not marked like a warlock is marked?”

Mortmain’s eyes sparkled with malevolence. “Indeed, why are you not? Perhaps because your mother had no idea what she was, any more than you do.”

“What do you mean? My mother was human!”

Mortmain shook his head. “Miss Gray, you continue to ask the wrong questions. What you must understand is that much was planned so that you would someday come to be. The planning began even before me—and I carried it forward, knowing I was overseeing the creation of something unique in the world. Something unique that would belong to me. I knew that I would one day marry you, and you would be mine forever.”

Tessa looked at him in horror. “But why? You don’t love me. You don’t know me. You didn’t even know what I looked like! I could have been hideous!”

“It would not have mattered. You can appear as hideous or as beautiful as you like. The face you wear now is only one of a thousand possible faces. When will you learn that there is no real Tessa Gray?”

“Get out,” Tessa said.

Mortmain looked at her with his pale eyes. “What did you say to me?”

“Get out. Leave the Institute. Take your monsters with you. Or I will stab myself in the heart.”

For a moment he hesitated, his hands clenching and unclenching at his sides. This must have been what he was like when forced to make a lightning-swift business decision—to buy or to sell? To invest or to expand? He was a man used to sizing up the situation in an instant, Tessa thought. And she was only a girl. What chance did she have to outmaneuver him?

Slowly he shook his head. “I don’t believe you’ll do it. You may be a warlock, but you’re still a young girl. A delicate female.” He took a step toward her. “Violence is not in your nature.”

Tessa gripped the handle of the knife tightly. She could feel everything—the hard slick surface under her fingers, the pain where it pierced her skin, the beat of her own heart. “Don’t come a step closer,” she said in a shaking voice, “or I’ll do it. I’ll drive the knife in.”

The tremble in her voice seemed to give him conviction; his jaw firmed, and he moved toward her with a confident stride. “No, you won’t.”

Tessa heard Will’s voice in her head. She took poison rather than let herself be captured by the Romans. She was braver than any man.

“Yes,” she said. “I will.”

Something in her face must have changed, for the confidence went from his expression and he lunged toward her, his arrogance gone, reaching desperately for the knife. Tessa spun away from Mortmain, turning to face the fountain. The last thing she saw was the silvery water splashing high above her as she drove the knife toward her chest.

Will was breathless as he approached the doors of the Sanctuary. He had fought two of the clockwork automatons in the stairwell and had thought he was done for, until the first one—having been run through several times with Thomas’s sword—began to malfunction and pushed the second creature out a window before collapsing and crashing down the stairs in a whirlwind of crumpling metal and shooting sparks.

Will had cuts on his hands and arms from the creatures’ jagged metal hides, but he had not slowed down for an iratze. He drew out his stele as he ran, and hit the Sanctuary doors at a dead run. He slashed the stele across the doors’ surface, creating the fastest Open rune of his life.

The doors’ lock slid back. Will took a split second of time to switch his stele for one of the seraph blades on his belt. “Jerahmeel,” he whispered, and as the blade blazed up with white fire, he kicked the Sanctuary doors open.

And froze in horror. Tessa lay crumpled by the fountain, whose water was stained with red. The front of her blue and white dress was a sheet of scarlet, and blood spread from beneath her body in a widening pool. A knife lay by her limp right hand, its hilt smeared with blood. Her eyes were closed.

Mortmain knelt by her side, his hand on her shoulder. He glanced up as the doors burst open, and then staggered to his feet, backing away from Tessa’s body. His hands were red with blood, and his shirt and jacket were stained with it.

“I … ,” he began.

“You killed her,” Will said. His voice sounded stupid to his own ears, and very far away. He saw again in his mind’s eye the library of the house he had lived in with his family as a child. His own hands on the box, curious fingers unclasping the catch that held it closed. The library filled with the sound of screaming. The road to London, silver in the moonlight. The words that had gone through his head, over and over, as he’d walked away from everything he had ever known, forever. I have lost everything. Lost everything.