Cristina handed Emma’s stele back to her. “I always wanted a parabatai,” she said a little wistfully. “Someone who is sworn to protect you and to watch your back. A best friend forever, for your whole life.”

A best friend forever, for your whole life. When Emma’s parents had died, she’d fought to stay with the Blackthorns. Partly because she’d lost everything familiar to her and she couldn’t bear the thought of starting over, and partly because she’d wanted to stay in Los Angeles so that she could investigate her parents’ deaths.

It might have been awkward; she might have felt, the only Carstairs in a house of Blackthorns, out of place in the family. But she never had, because of Jules. Parabatai was more than friendship, more than family; it was a bond that tied you together, fiercely, in a way that every Shadowhunter respected and acknowledged the way that they respected the bond between husband and wife.

No one would separate parabatai. No one would dare try: Parabatai were stronger together. They fought together as if they could read each other’s minds. A single rune given to you by your parabatai was more powerful than ten runes given to you by someone else. Often parabatai had their ashes buried in the same tomb so that they wouldn’t be parted, even in death.

Not everyone had a parabatai; in fact, they were rare. It was a lifelong, binding commitment. You were swearing to stay by the other person’s side, swearing to always protect them, to go where they went, to consider their family your family. The words of the oath were from the Bible, and ancient: Whither thou goest, I will go; thy people shall be my people; where thou diest, will I die, and there will I be buried.

If there was a term for it in mundane English, Emma thought, it would have been “soul mate.” Platonic soul mate. You weren’t allowed to be romantically involved with your parabatai. Like so many things, it was against the Law. Emma had never known why—it didn’t make any sense—but then, much of the Law didn’t. It hadn’t made sense for the Clave to exile and abandon Julian’s half siblings, Helen and Mark, simply because their mother had been a faerie, but they’d done that too when they’d created the Cold Peace.

Emma stood up, sliding her stele into her weapons belt. “Well, the Blackthorns are coming back the day after tomorrow. You’ll meet Jules then.” She moved back toward the edge of the roof, and this time she heard the scrape of boots on tile that told her Cristina was behind her. “Do you see anything?”

“Maybe there’s nothing going on.” Cristina shrugged. “Maybe it’s just a party.”

“Johnny Rook was so sure,” muttered Emma.

“Didn’t Diana specifically forbid you to go see him?”

“She may have told me to stop seeing him,” Emma acknowledged. “She may even have called him ‘a criminal who commits crime,’ which I have to say struck me as harsh, but she didn’t say I couldn’t go to the Shadow Market.”

“Because everyone already knows Shadowhunters aren’t meant to go to the Shadow Market.”

Emma ignored this. “And if I ran into Rook, say, at the Market, and he dropped some information while we were chatting and I accidentally let drop some money, who’s to call that ‘paying for information’? Just two friends, one careless with his gossip and the other one careless with her finances . . .”

“That’s not the spirit of the Law, Emma. Remember? The Law is hard, but it is the Law.”

“I thought it was ‘the Law is annoying, but it is also flexible.’”

“That is not the motto. And Diana is going to kill you.”

“Not if we solve the murders, she won’t. The ends will justify the means. And if nothing happens, she never has to know about it. Right?”

Cristina didn’t say anything.

“Right . . . ?” Emma said.

Cristina gave an intake of breath. “Do you see?” she asked, pointing.

Emma saw. She saw a tall man, handsome and smooth-haired, with pale skin and carefully tailored clothes, moving among the crowd. As he went, men and women turned to look after him, their faces slack and fascinated.

“There is a glamour on him,” Cristina said. Emma quirked an eyebrow. Glamour was illusion magic, commonly used by Downworlders to hide themselves from mundane eyes. Shadowhunters also had access to Marks that had much the same effect, though Nephilim didn’t consider that magic. Magic was warlock business; runes were a gift from the Angel. “The question is, vampire or fey?”

Emma hesitated. The man was approaching a young woman in towering heels, a glass of champagne in her hand. Her face went smooth and blank as he spoke to her. She nodded agreeably, reached up, and undid the chunky gold necklace she was wearing. She dropped it into his outstretched hand, a smile on her face as he slid it into his pocket.

“Fey,” Emma said, reaching for her weapons belt. Faeries complicated everything. According to the Law of the Cold Peace, an underage Shadowhunter shouldn’t have anything to do with faeries at all. Faeries were off-limits, the cursed and forbidden branch of Downworlders, ever since the Cold Peace, which had ripped away their rights, their armies, and their possessions. Their ancient lands were no longer considered theirs, and other Downworlders fought over who could claim them. Trying to calm such battles was a great part of the business of the Los Angeles Institute, but it was adult business. Shadowhunters Emma’s age weren’t meant to engage directly with faeries.

In theory.

The Law is annoying, but it is flexible. Emma drew a small cloth bag, tied at the top, out of a pouch attached to her belt. She began to flick it open as the fey moved from the smiling woman to a slender man in a black jacket, who willingly handed over his sparkling cuff links. The fey was now standing almost directly beneath Emma and Cristina. “Vampires don’t care about gold, but the Fair Folk pay tribute to their King and Queen in gold and gems and other treasure.”

“I have heard the Court of the Unseelie pays it in blood,” said Cristina grimly.

“Not tonight,” Emma said, flicking the bag she was holding open and upending the contents onto the faerie’s head.

Cristina gasped in horror as the fey below them gave a hoarse cry, his glamour falling away from him like a snake shedding its skin.

A chorus of shrieks went up from the crowd as the fey’s true appearance was revealed. Branches grew like twisted horns from his head, and his skin was the dark green of moss or mildew, cracked all over like bark. His hands were spatulate claws, three-fingered.

“Emma,” Cristina warned. “We should stop this now—call the Silent Brothers—”

But Emma had already jumped.

For a moment she was weightless, falling through the air. Then she struck the ground, knees bent as she’d been taught. How she remembered those first jumps from great heights, the snapping, awkward falls, the days she’d have to wait to heal before trying again.

No longer. Emma rose to her feet, facing the faerie across the fleeing crowd. Gleaming from his weathered, barklike face, his eyes were yellow as a cat’s. “Shadowhunter,” he hissed.

The partygoers continued to flee from the courtyard through the gates that led into the parking lot. None of them saw Emma, though their instincts kicked in anyway, making them pass around her like water around the pilings of a bridge.