She looked past the man to the coach behind him—and froze. Instead of a coat of arms, the name of a business enterprise was painted across one of the doors: MORTMAIN AND COMPANY.

Mortmain. The man her father had worked for, whom Nathaniel had blackmailed, who had introduced her brother to the Shadow World. What was he doing here?

She looked at Nate again, her feeling of annoyance washed away by a wave of protectiveness. If he knew Mortmain was here, he would doubtless be upset. It would be better if she found out what was going on before he did. She slid off the windowsill and made her way quietly to the door; deep in conversation with Jessamine, Nate hardly seemed to notice as she left the room.

It was surprisingly easy for Tessa to find her way to the huge stone-bound spiral stairway that speared through the center of the Institute. She must have been learning her way around the place at last, she decided as she made her way down the steps to the ground floor, and found Thomas standing in the entryway.

He was holding a massive sword, point down, his face very serious. Behind him the massive double doors of the Institute were open on a rectangle of blue-black London twilight, lit by the blaze of the courtyard’s witchlight torches. He looked taken aback at the sight of Tessa. “Miss Gray?”

She pitched her voice low. “What’s going on out there, Thomas?”

He shrugged. “Mr. Mortmain,” he said. “He wanted to speak with Mr. and Mrs. Branwell, but since they’re not here—”

Tessa started toward the door.

Thomas, startled, moved to prevent her. “Miss Gray, I don’t think—”

“You’ll have to use that sword on me to stop me, Thomas,” Tessa said in a cold voice, and Thomas, after a moment’s hesitation, moved aside. Tessa, with a twinge, hoped she hadn’t hurt his feelings, but he looked more astonished than anything else.

She moved past him, onto the steps outside the Institute, where Will and Jem were standing. A hard breeze was coming up, ruffling her hair and making her shiver. At the foot of the stairs stood the man she had seen from the window. He was shorter than she would have imagined: small and wiry-looking, with a tanned, friendly face beneath the brim of his tall hat. Despite the elegance of his clothes, he had the bluff, natural bearing of a sailor or tradesman.

“Yes,” he was saying, “Mr. and Mrs. Branwell were kind enough to call on me last week. And were even kinder, I understand, in keeping our meeting something of a secret.”

“They didn’t tell the Enclave about your occult experimentations, if that is what you mean,” Will said a bit shortly.

Mortmain reddened. “Yes. It was a favor. And I had thought to return the favor in kind—” He broke off, looking past Will at Tessa. “And who is this? Another Shadowhunter?”

Will and Jem both turned at the same time and saw Tessa. Jem looked pleased to see her; Will, of course, looked exasperated, and perhaps a touch amused. “Tessa,” he said. “Couldn’t keep your nose out, could you?” He turned back to Mortmain. “This is Miss Gray, of course. Nathaniel Gray’s sister.”

Mortmain looked appalled. “Oh, good God. I should have realized. You look like him. Miss Gray—”

“I don’t think she does, actually,” Will said, but rather quietly, so Tessa doubted Mortmain could hear him.

“You can’t see Nate,” Tessa said. “I don’t know if that’s why you’ve come here, Mr. Mortmain, but he isn’t well enough. He needs to recover from his ordeal, not be reminded of it.”

The lines deepened at the corners of Mortmain’s mouth. “I’m not here to see the boy,” he said. “I recognize that I failed him, failed him abominably. Mrs. Branwell made that clear—”

“You should have looked for him,” Tessa said. “My brother. You let him sink into the Shadow World without a trace.” Some small part of Tessa’s mind was amazed she was being so bold, but she went on, regardless. “When he told you he’d gone to work for de Quincey, you should have done something. You knew what kind of man de Quincey was—if you can even call him a man.”

“I know.” Mortmain looked gray beneath his hat. “That is why I am here. To try to make up for what I’ve done.”

“And how do you propose to do that?” asked Jem, in his clear, strong voice. “And why now?”

Mortmain looked at Tessa. “Your parents,” he said, “were good, kind people. I have always regretted introducing them to the Shadow World. At the time, I thought it all a delightful game and a bit of a joke. I have learned otherwise since. To assuage that guilt, I will tell you what I know. Even if it means I must flee England to escape de Quincey’s wrath.” He sighed. “Some time ago, de Quincey ordered from me a number of mechanical parts—cogs, cams, gears, and the like. I never asked what he needed them for. One does not inquire such things of the Magister. Only when you Nephilim came to see me did it occur to me that his need for them might be connected to a nefarious purpose. I investigated, and an informant within the club told me that de Quincey intended to build an army of mechanical monsters meant to destroy the ranks of Shadowhunters.” He shook his head. “De Quincey and his ilk may despise Shadowhunters, but I do not. I am only a human man. I know they are all that stand between me and a world in which I and my kind are the playthings of demons. I cannot stand behind what de Quincey is doing.”

“That is all very well,” Will said, a hint of impatience in his voice, “but you are not telling us anything we do not already know.”

“Did you also know,” Mortmain said, “that he paid a pair of warlocks called the Dark Sisters to create a binding spell that would animate these creatures not with mechanics but with demonic energies?”

“We did,” said Jem. “Though I believe there is only one Dark Sister remaining. Will destroyed the other one.”

“But her sister brought her back via a necromantic charm,” said Mortmain, a hint of triumph in his tone, as if he were relieved to at last have a piece of information that they did not. “Even now the two of them are ensconced in a mansion in Highgate—it used to belong to a warlock, until de Quincey had him killed—working on the binding spell. If my sources are correct, the Dark Sisters will attempt to implement the spell tonight.”

Will’s blue eyes were dark and thoughtful. “Thank you for the information,” he said, “but de Quincey will soon be no more of a threat to us, or his mechanical monsters, either.”

Mortmain’s eyes widened. “Is the Clave to move against the Magister? Tonight?”

“Goodness,” said Will. “You really do know all the terms, don’t you. It’s very disconcerting in a mundane.” He smiled pleasantly.

“You mean you’re not going to tell me,” said Mortmain ruefully. “I suppose you wouldn’t. But you should know that de Quincey has at his disposal hundreds of those clockwork creatures. An army. The moment the Dark Sisters work their spell, the army will rise and join with de Quincey. If the Enclave is to defeat him, it would be wise to ensure that that army does not rise, or they will be nearly impossible to defeat.”

“Are you aware of the Dark Sisters’ location, beyond the fact that it is in Highgate?” asked Jem.

Mortmain nodded. “Most certainly,” he said, and rattled off a street name and house number.

Will nodded. “Well, we’ll certainly take all this under advisement. Thank you.”

“Indeed,” said Jem. “Good evening, Mr. Mortmain.”

“But—” Mortmain looked taken aback. “Are you going to do something about what I’ve told you, or not?”

“I said we’d take it under advisement,” Will told him. “As for you, Mr. Mortmain, you look like a man with somewhere to be.”

“What?” Mortmain glanced down at his evening dress, and chuckled. “I suppose so. It’s just—if the Magister finds out that I’ve told you all this, my life could be in danger.”

“Then perhaps it is time for a holiday,” Jem suggested. “I’ve heard Italy is very pleasant this time of year.”

Mortmain looked from Will to Jem and back again, and then seemed to give up. His shoulders sagged. He raised his eyes to Tessa. “If you could pass along my apologies to your brother …”

“I don’t think so,” Tessa said, “but thank you, Mr. Mortmain.”

After a long pause he nodded, then turned away. The three of them watched as he climbed back into his carriage. The sound of the horses’ hooves was loud in the courtyard as the carriage pulled away and rattled through the Institute gates.

“What are you going to do?” Tessa asked the moment the carriage was out of sight. “About the Dark Sisters?”

“Go after them, of course.” Will’s color was high, his eyes glittering. “Your brother said de Quincey had dozens of those creatures at his disposal; Mortmain says there are hundreds. If Mortmain’s correct, we must get to the Dark Sisters before they work their spell, or the Enclave may well be walking into a slaughter.”

“But—perhaps it would be better to warn Henry and Charlotte and the others—”

“How?” Will managed to make the one word sound cutting. “I suppose we could send Thomas to warn the Enclave, but there is no guarantee he will get there in time, and if the Dark Sisters manage to raise the army, he could simply be killed with the rest. No, we must manage the Dark Sisters on our own. I killed one of them before; Jem and I ought to be able to manage two.”

“But perhaps Mortmain is wrong,” Tessa said. “You have only his word; he might have faulty information.”

“He might,” Jem acknowledged, “but can you imagine if he doesn’t? And we ignored him? The consequence to the Enclave could be utter destruction.”

Tessa, knowing he was right, felt her heart sink. “Maybe I could help. I fought the Dark Sisters with you once before. If I could accompany you—”

“No,” Will said. “It’s out of the question. We have so little time to prepare that we must rely on our fighting experience. And you have none.”

“I fought off de Quincey at the party—”

“I said no.” Will’s tone was final. Tessa looked at Jem, but he gave only an apologetic shrug as if to say that he was sorry but Will was right.

She turned her gaze back to Will. “But what about Boadicea?”

For a moment she thought he’d forgotten what he’d said to her in the library. Then the glimmer of a smile tugged at the corner of his mouth, as if he’d tried to fight it and couldn’t. “You will be Boadicea someday, Tessa,” he said, “but not tonight.” He turned to Jem. “We ought to get Thomas and tell him to ready the carriage. Highgate’s not close; we’d best get started.”

Full night had descended on the city by the time Will and Jem stood out by the carriage, preparing to depart. Thomas was checking the fastenings on the horses while Will, his stele a white flash in the dimness, scrawled a Mark on Jem’s bare forearm. Tessa, having registered her disapproval, stood on the steps and watched them, a hollow feeling in her stomach.