“Clary,” Jace said, a warning in his voice.

Clary shot a look at him over her shoulder; surely telling Mark his siblings were alive was the most important thing?

“Have you eaten anything, drunk anything since the Fair Folk took you?” Jace asked, moving to peer into Mark’s face. Mark jerked away, but not before Clary heard Jace’s sharp intake of breath.

“What is it?” Isabelle demanded.

“His eyes,” Jace said, raising his witchlight and shining it into Mark’s face. Mark scowled again but allowed Jace to examine him.

His eyes were large, long-lashed, like Helen’s; unlike hers, his were mismatched. One was Blackthorn blue, the color of water. The other was gold, hazed through with shadows, a darker version of Jace’s own.

Jace swallowed visibly. “The Wild Hunt,” he said. “You’re one of them now.”

Jace was scanning the boy with his eyes, as if Mark were a book he could read. “Put your hands out,” Jace said finally, and Mark did so. Jace caught them and turned them over, baring the other boy’s wrists. Clary felt her throat tighten. Mark was wearing only a T-shirt, and his bare forearms were striped with bloody whip marks. Clary thought of the way she had touched Mark’s shoulder and he’d flinched away. God knew what his other injuries were, under his clothes. “When did this happen?”

Mark pulled his hands away. They were shaking. “Meliorn did it,” he said. “When he first took me. He said he’d stop if I ate and drank their food, so I did. I didn’t think it mattered, if my family was dead. And I thought faeries couldn’t lie.”

“Meliorn can,” said Alec grimly. “Or at least, he could.”

“When did this all happen?” Isabelle demanded. “The faeries only took you less than a week ago—”

Mark shook his head. “I’ve been with the Folk for a long time,” he said. “I couldn’t say how long.”

“Time runs differently in Faerie,” Alec said. “Sometimes faster, sometimes slower.”

Mark said, “Gwyn told me I belonged to the Hunt and I couldn’t leave them unless they allowed me to go. Is that true?”

“It’s true,” Jace said.

Mark slumped against the cave wall. He turned his head toward Clary. “You saw them. You saw my brothers and sisters. And Emma?”

“They’re all right, all of them, Emma, too,” Clary said. She wondered if it helped. He had sworn to stay in Faerie because he thought his family was dead, and the promise held, though it was based on a lie. Was it better to think you had lost everything, and to start over? Or easier to know that the people you loved were alive, even if you could never see them again?

She thought of her own mother, somewhere in the world beyond the end of the tunnel. Better to know they were alive, she thought. Better for her mother and Luke to be alive and all right, and for her never to see them again, than for them to be dead.

“Helen can’t take care of them. Not alone,” Mark said a little desperately. “And Jules, he’s too young. He can’t take care of Ty; he doesn’t know the things he needs. He doesn’t know how to talk to him—” He took a shuddering breath. “You should let me come with you.”

“You know you can’t,” said Jace, though he couldn’t look Mark in the face; he was staring at the ground. “If you’ve sworn fealty to the Wild Hunt, you’re one of them.”

“Take me with you,” Mark repeated. He had the stunned, bewildered look of someone who had been mortally injured but didn’t yet realize the extent of the injury. “I don’t want to be one of them. I want to be with my family—”

“We’re going to Hell,” Clary said. “We couldn’t bring you with us, even if you could leave Faerie safely—”

“And you can’t,” Alec said. “If you try to leave, you’ll die.”

“I’d rather die,” Mark said, and Jace’s head whipped up. His eyes were bright gold, almost too bright, as if the fire inside him were spilling out through them.

“They took you because you have faerie blood, but also because you have Shadowhunter blood. They want to punish the Nephilim,” Jace said, his gaze intent. “Show them what a Shadowhunter is made of; show them you aren’t afraid. You can live through this.”

In the wavering illumination of the witchlight, Mark looked at Jace. Tears had made their tracks through the dirt on his face, but his eyes were dry. “I don’t know what to do,” he said. “What do I do?”

“Find a way to warn the Nephilim,” Jace said. “We’re going into Hell, like Clary said. We might never come back. Someone has to tell the Shadowhunters the Fair Folk are not their allies.”

“The Hunters will catch me if I try to send a message.” The boy’s eyes flashed. “They’ll kill me.”

“Not if you’re fast and smart,” said Jace. “You can do it. I know you can.”

“Jace,” Alec said, his bow at his side. “Jace, we need to let him go before the Hunt notice he’s missing.”

“Right,” Jace said, and hesitated. Clary saw him take Mark’s hand; he pressed his witchlight into the boy’s palm, where it flickered, and then resumed its steady glow. “Take this with you,” said Jace, “for it can be dark in the land under the hill, and the years very long.”

Mark stood for a moment, the rune-stone in his hand. He looked so slight in the wavering light that Clary’s heart hammered a tattoo of disbelief—surely they could help him, they were Nephilim, they didn’t leave their own behind—and then he turned and ran, away from them, on soundless bare feet.

“Mark—” Clary whispered, and cut herself off; he was gone. The shadows swallowed him up, only the darting will-o’-the-wisp light of the rune-stone visible, until it too blended with the darkness. She looked up at Jace. “What did you mean, ‘the land under the hill’?” she asked. “Why did you say that?”

Jace didn’t answer her; he looked stunned. She wondered if Mark, brittle and orphaned and alone, reminded him somehow of himself.

“The land under the hill is Faerie,” said Alec. “An old, old name for it. He’ll be all right,” he said to Jace. “He will.”

“You gave him your witchlight,” Isabelle said. “You’ve always had that witchlight—”

“Screw the witchlight,” Jace said violently, and slammed his hand against the wall of the cave; there was a brief flare of light, and he drew his arm back. The mark of his hand was burned black into the stone of the tunnel, and his palm still glowed, as if the blood in his fingers were phosphorus. He gave an odd, choked laugh. “I don’t exactly need it, anyway.”

“Jace,” Clary said, and put her hand on his arm. He didn’t move away from her, but he didn’t react, either. She dropped her voice. “You can’t save everyone,” she said.

“Maybe not,” he said as the light in his hand dimmed. “But it would be nice to save someone for a change.”

“Guys,” Simon said. He’d been oddly quiet throughout the encounter with Mark, and Clary was startled to hear him speak now. “I don’t know if you can see it, but there’s something—something at the end of the tunnel.”