He was leaning against the wal opposite her, between two empty chairs.

Despite his mask she felt as if she could see directly into his eyes. As if he were standing close enough to touch. She would have half-expected him to look amused at her predicament, but he did not; he looked tense, and furious, and . . .

"God, I'm jealous of every other man who looks at you," Nate said. "You should be looked at only by me."

Good Lord, Tessa thought. Did this line of talk really work on most women? If her brother had come to her with the aim of asking her advice on these pearls, she would have told him straight off that he sounded like an idiot. Though perhaps she only thought he sounded like an idiot because he was her brother. And despicable. Information, she thought. I must get information and then get away from him, before I really am sick.

She looked for Will again, but he was gone, as if he had never been there.

Still, she believed him now that he was somewhere, watching her, even if she couldn't see him. She plucked up her nerve, and said, "Real y, Nate? Sometimes I fear you value me only for the information I can give you."

For a moment he stopped and was stock-still, almost jerking her out of the dance. "Jessie! How can you even think such a thing? You know how I adore you." He looked at her reproachful y as they began to move to the music again. "It is true that your connection to the Nephilim of the Institute has been invaluable. Without you we would never have known they were going to York, for instance. But I thought you knew that you were helping me because we are working toward a future together. When I have become the Magister's right hand, darling, think how I Will be able to provide for you."

Tessa laughed nervously. "You're right, Nate. It's only that I get frightened sometimes. What if Charlotte were to find out I was spying for you? What would they do to me?"

Nate swung her around easily. "Oh, nothing, darling; you've said it yourself, they're cowards." He looked past her and raised an eyebrow. "Benedict, up to his old tricks," he said. "Rather disgusting."

Tessa looked around and saw Benedict Lightwood leaning back on a scarlet velvet sofa near the orchestra. He was coatless, a glass of red wine in one hand, his eyes half-lidded. Sprawled across his chest, Tessa saw to her shock, was a woman-or at least it had the form of a woman. Long black hair worn loose, a low-cut black velvet gown-and the heads of little serpents poking out from her eyes, hissing. As Tessa watched, one of them extended a long, forked tongue and licked the side of Benedict Lightwood's face.

"That's a demon," Tessa breathed, forgetting for a moment to be Jessamine. "Isn't it?"

Fortunately Nate seemed to find nothing odd about the question. "Of course it is, sil y bunny. That's what Benedict fancies. Demon women."

Will 's voice echoed in Tessa's ears, I would be surprised if some of the elder Lightwood's nocturnal visits to certain houses in Shadwell haven't left him with a nasty case of demon pox. "Oh, ugh," she said.

"Indeed," said Nate. "Ironic, considering the high-and-mighty manner in which the Nephilim conduct themselves. I ask myself often why Mortmain favors him so and wishes to see him instal ed in the Institute so badly." Nate sounded peevish.

Tessa had already guessed as much, but the knowledge that Mortmain was most assuredly behind Benedict's fierce determination to take the Institute from Charlotte still felt like a blow. "I just don't see," she said, trying her best to adopt Jessie's lightly peevish demeanor, "what use it Will be to the Magister. It's just a big stuffy old building. . . ."

Nate laughed indulgently. "It's not the building, sil y thing. It's the position.

The head of the London Institute is one of the most powerful Shadowhunters in England, and the Magister controls Benedict as if he were a puppet. Using him, he can destroy the Council from within, while the automaton army destroys them from without." He spun her expertly as the dance required; only Tessa's years of practice dancing with Nate kept her from fal ing over, so distracted was she by shock. "Besides, it's not quite true that the Institute contains nothing of value. Access to the Great Library alone Will be invaluable for the Magister. Not to mention the weapons room . . ."

"And Tessa." She clamped down on her voice so it wouldn't tremble.

"Tessa?"

"Your sister. The Magister still wants her, doesn't he?"

For the first time Nate looked at her with a puzzled surprise. "We've been over this, Jessamine," he said. "Tessa Will be arrested for il egal possession of articles of dark magic, and sent to the Silent City. Benedict Will bring her forth from there and deliver her to the Magister. It is all part of whatever bargain they struck, though what Benedict is getting from it is not clear to me yet. It must be something quite significant, or he would not be so Will ing to turn on his own."

A rrested? Possession of articles of dark magic? Tessa's head spun.

Nate's hand slipped around the back of her neck. He was wearing gloves, but Tessa couldn't rid herself of the feeling that something slimy was touching her skin. "My little Jessie," he murmured. "You behave almost as if you've forgotten your own part in this. You did hide the Book of the White in my sister's room as we asked you to, did you not?"

"Of-of course I did. I was only joking, Nate."

"That's my good girl." He was leaning closer. He was definitely going to kiss her. It was most improper, but then nothing about this place could be considered proper. In a state of absolute horror, Tessa sputtered: "Nate-I feel dizzy-as if I might faint. I think it's the heat. If you could fetch me a lemonade?"

He looked down at her for a moment, his mouth tight with bottled annoyance, but Tessa knew he could not refuse. No gentleman would. He straightened up, brushed off his cuffs, and smiled. "Of course," he said with a bow. "Let me help you to a seat first."

She protested, but his hand was already on her elbow, guiding her toward one of the chairs lined up along the wal s. He settled her into it and vanished into the crowd. She watched him go, trembling all over. Dark magic. She felt sick, and angry. She wanted to slap her brother, shake him til he told her the rest of the truth, but she knew she couldn't.

"You must be Tessa Gray," said a soft voice at her elbow. "You look just like your mother."

Tessa nearly jumped out of her skin. At her side stood a tal slender woman with long, unbound hair the color of lavender petals. Her skin was a pale blue, her dress a long and floating confection of gossamer and tul e. Her feet were bare, and in between her toes were thin webs like a spider's, a darker blue than her skin. Tessa's hands went to her face in sudden horror- was she losing her disguise?-but the blue woman laughed.

"I didn't mean to make you fearful of your il usion, little one. It is still in place. It is just that my kind can see through it. all this"-she gestured vaguely at Tessa's blond hair, her white dress and pearls-"is like the vapor of a cloud, and you the sky beyond it. Did you know your mother had eyes just like yours, gray sometimes and blue at others?"

Tessa found her voice. "Who are you?"

"Oh, my kind doesn't like to give our names, but you can call me whatever you like. You can invent a lovely name for me. Your mother used to call me Hyacinth."

"The blue flower," Tessa said faintly. "How did you know my mother? You don't look any older than me-"

"After our youth, my kind does not age or die. Nor Will you. Lucky girl! I hope you appreciate the service done you."

Tessa shook her head in bewilderment. "Service? What service? Are you speaking of Mortmain? Do you know what I am?"

"Do you know what I am?"

Tessa thought of the Codex. "A faerie?" she guessed.

"And do you know what a changeling is?"

Tessa shook her head.

"Sometimes," Hyacinth confided, dropping her voice to a whisper, "when our faerie blood has grown weak and thin, we Will find our way into a human home, and take the best, the prettiest, and the plumpest child-and, quick as a wink, replace the babe with a sickly one of our own. While the human child grows tal and strong in our lands, the human family Will find itself burdened with a dying creature fearful of cold iron. Our bloodline is strengthened-"

"Why bother?" Tessa demanded. "Why not just steal the human child and leave nothing in its place?"

Hyacinth's dark blue eyes widened. "Why, because that would not be fair,"

she said. "And it would breed suspicion among the mundanes. They are stupid, but there are many of them. It does not do to rouse their ire. That is when they come with iron and torches." She shuddered.

"Just a moment," Tessa said. "Are you tell ing me I'm a changeling?"

Hyacinth bubbled over with giggles. "Of course not! What a ridiculous thought!" She held her hands to her heart as she laughed, and Tessa saw that her fingers, too, were bound together with blue webbing. Suddenly she smiled, showing glittering teeth. "There's a very good-looking boy staring over here," she said. "As handsome as a faerie lord! I should leave you to your business." She winked, and before Tessa could protest, Hyacinth melted back into the crowd.

Shaken, Tessa turned, expecting the "good-looking boy" to be Nate-but it was Will, leaning against the wal beside her. The moment her eyes found him, he turned and began studiously examining the dance floor. "What did that faerie woman want?"

"I don't know," Tessa said, exasperated. "To tell me I'm not a changeling, apparently."

"Well, that's good. Process of elimination." Tessa had to admit, Will was doing a good job of somehow blending in with the dark curtains behind him, as if he were not there at all. It must have been a Shadowhunter talent. "And what news from your brother?"

She gripped her hands together, looking at the floor while she spoke.

"Jessamine's been spying for Nate all this time. I don't know how long exactly. She's been tell ing him everything. She thinks he's in love with her."

Will looked unsurprised. "Do you think he's in love with her?"

"I think Nate cares only about himself," said Tessa. "There's worse, too.

Benedict Lightwood is working for Mortmain. That is why he is scheming to get the Institute. So the Magister can have it. And have me. Nate knows all about it, of course. He doesn't care." Tessa looked at her hands again.

Jessamine's hands. Smal and delicate in their fine white kid gloves. Oh, Nate, she thought. A unt Harriet used to call him her blue-eyed boy.

"I expect that was before he kil ed her," said Will. Only then did Tessa realize she had spoken aloud. "And there he is again," he added, in a mutter, under his breath. Tessa glanced out at the crowd and saw Nate, his fair hair like a beacon, coming toward her. In his hand was a glass of sparkling golden liquid. She turned to tell Will to hurry away, but he had already vanished.

"Fizzy lemonade," said Nate, coming up to her and thrusting the glass into her hand. The ice-cold sides felt good against the heat of her skin. She took a sip; despite everything, it was delicious.

Nate stroked her hair back from her forehead. "Now, you were saying," he said. "You did hide the book in my sister's room . . ."

"Yes, just as you told me to do," Tessa fibbed. "She suspects nothing, of course."

"I should hope not."

"Nate . . ."

"Yes?"

"Do you know what the Magister intends to do with your sister?"

"I've told you, she isn't my sister." Nate's voice was clipped. "And I've no idea what he plans to do with her, nor any interest. My plans are all for my -our future together. I should hope that you are as dedicated?" Tessa thought of Jessamine, sitting sul enly in the room with the other Shadowhunters while they shuffled through papers about Mortmain; Jessamine fal ing asleep at the table rather than leave when they were discussing plans with Ragnor Fell. And Tessa pitied her even as she hated Nate, hated him so much it felt like fire in her throat. I've told you, she isn't my sister.

Tessa let her eyes widen, her lip tremble. "I'm doing the best I can, Nate,"

she said. "Don't you believe me?"

She felt a faint sense of triumph as she watched him visibly beat back his annoyance. "Of course, darling. Of course." He examined her face. "Are you feeling better? shall we dance again?"

She clutched the glass in her hand. "Oh, I don't know . . ."

"Of course," Nate chuckled, "they do say a gentleman should dance only the first set or two with his wife."

Tessa froze. It was as if time had stopped: Everything in the room seemed to freeze along with her, even the smirk on Nate's face.

Wife?

He and Jessamine were married?

"Angel?" said Nate, his voice sounding as if it were coming from far away.

"Are you all right? You've gone white as a sheet."

"Mr. Gray." A dull, mechanical voice spoke from behind Nate's shoulder. It was one of the blank-faced automatons, holding out a silver tray on which was a folded piece of paper. "A message for you."

Nate turned in surprise and plucked the paper from the tray; Tessa watched as he unfolded it, read it, cursed, and stuffed it into his coat pocket.

"My, my," he said. "A note from himself." He must mean the Magister, Tessa thought. "I'm needed apparently. A dreadful bore, but what can you do?" He took her hand and raised her to her feet, then leaned in for a chaste kiss on the cheek. "Speak to Benedict; he'l make sure you're escorted back out to the carriage, Mrs. Gray." He spoke the last two words in a whisper.

Tessa nodded numbly.

"Good girl," Nate said. Then he turned and vanished into the crowd, fol owed by the automaton. Tessa stared after them both dizzily. It must be the shock, she thought, but everything in the room had begun to look a little- peculiar. It was as if she could see each individual ray of light sparking off the crystals of the chandelier. The effect was beautiful, if strange and a little dizzying.

"Tessa." It was Will, evolving effortlessly into the space beside her. She turned to look at him. He looked flushed, as if he had been running-another beautiful, strange effect, she thought, the black hair and mask, the blue eyes and fair skin, and the flush across his high cheekbones. It was like looking at a painting. "I see your brother got the note."