“He’s a book character,” Dru said, laughing.

“I’ve got all the Sherlock Holmes books,” said Ty. “I know all the stories. There are fifty-six short stories and four novels. I can tell them to you. And I’ll show you how to use the microscope.”

“I think I buttered it,” Mark admitted, looking shamefaced. “I did not remember it was a scientific tool.”

Emma looked worriedly at Ty—he was meticulous about his things and could be deeply upset by anyone touching them or moving them. But he didn’t look angry. Something about Mark’s candidness seemed to delight him, the way he sometimes was delighted by an unusual kind of demonic ichor or the life cycle of bees.

Mark had cut his apple into careful pieces and was eating them slowly, in the manner of someone who was used to making what food they had last. He was quite thin, thinner than a Shadowhunter his age would usually be—Shadowhunters were encouraged to eat and train, eat and train, build their muscle and stamina. Most Shadowhunters, due to the constant brutal physical training, ranged from wiry to muscular, though Drusilla was round-bodied, something that bothered her more the older she got. Emma always felt pained to see the blush that colored Dru’s cheeks when the gear designated for girls in her age group didn’t fit.

“I heard you speak of convergences,” Mark said, moving toward the others—carefully, as if unsure of his welcome. His eyes lifted, and to Emma’s surprise, he looked at Cristina. “The convergence of ley lines is a place where dark magic can be done undetected. The Fair Folk know much of ley lines, and use them often.” He had slung his arrowhead back around his neck; it glimmered as he bent his head to look at the map on the table.

“This is a map of ley lines in Los Angeles,” said Cristina. “All of the bodies have been found along them.”

“Wrong,” Mark said, leaning forward.

“No, she’s right,” Ty said with a frown. “It is a map of ley lines, and the bodies have been dumped along them.”

“But the map is incorrect,” Mark said. “The lines are not accurate, nor are the points of convergence.” His long-fingered right hand brushed over the pencil circle Ty had made. “This is not right at all. Who made this map?”

Julian moved closer and for a moment he and his brother were shoulder to shoulder, their pale hair and dark hair a startling contrast. “It’s the Institute’s map, I assume.”

“We took it from the trunk,” Emma said, leaning over it from the opposite side of the table. “With all the other maps.”

“Well, it has been tampered with,” said Mark. “We will need a correct one.”

“Maybe Diana could get us one,” Julian said, reaching for a pad of paper and a pencil. “Or we could ask Malcolm.”

“Or check out what’s at the Shadow Market,” said Emma, and grinned unrepentantly at Julian’s look. “Just a suggestion.”

Mark glanced at his brother, and then the others, clearly worried. “Was that helpful?” he said. “Was it a thing I should not have said?”

“Are you sure?” said Ty, looking from the map to his brother, and something in his face was open as a door. “That the map is incorrect?”

Mark nodded.

“Then it was helpful,” said Ty. “We could have wasted days on a map that was wrong. Maybe longer.”

Mark exhaled in relief. Julian put his hand on Mark’s back. Livvy and Dru beamed. Tavvy was looking out from under the table, clearly curious. Emma glanced at Cristina. The Blackthorns seemed to be wound together by a sort of invisible force; in that moment they were completely a family, and Emma could not even mind that she and Cristina were on the outside.

“I could attempt to correct it,” said Mark. “But I do not know if I have the skill. Helen—Helen could do it.” He glanced at Julian. “She is married, and away—but I assume she will return for this? And to see me?”

It was like watching glass shatter in slow motion. None of the Blackthorns moved, not even Tavvy, but blankness spread over their features as they realized exactly how much it was that Mark did not know.

Mark paled and slowly set the core of his apple down on the table. “What is it?”

“Mark,” Julian said, looking toward the door, “come and talk to me in your room, not here—”

“No,” Mark interrupted, his voice rising with fear. “You will tell me now. Where is my full-blood sister, the daughter of Lady Nerissa? Where is Helen?”

There was an achingly awkward silence. Mark was looking at Julian; they were no longer standing beside each other. Mark had moved away, so quietly and quickly Emma had not seen it happen. “You said she was alive,” he said, and in his voice there was fear and accusation.

“She is,” Emma hastened to say. “She’s fine.”

Mark made an impatient noise. “Then I would know where my sister is. Julian?”

But it wasn’t Julian who answered. “She was sent away when the Cold Peace was decided,” Ty said, to Emma’s surprise. He sounded matter-of-fact. “She was exiled.”

“There was a vote,” said Livvy. “Some of the Clave wanted to kill her, because of her faerie blood, but Magnus Bane defended the rights of Downworlders. Helen was sent to Wrangel Island to study the wards.”

Mark leaned against the table, his palm flat against it, as if he were trying to catch his breath after being punched. “Wrangel Island,” he whispered. “It is a cold place, ice and snow. I have ridden over those lands with the Hunt. I never knew my sister was down there, in among the frozen wastes.”

“They would never have let you see her, even if you had known,” Julian said.

“But you let her be sent away.” Mark’s two-colored eyes were flashing. “You let them exile her.”

“We were children. I was twelve years old.” Julian didn’t raise his voice; his blue eyes were flat and cold. “We had no choice. We talk to Helen every week, we petition the Clave every year for her return.”

“Speech and petitions,” Mark spat. “Might as well do nothing. I knew—I knew they had chosen not to come for me. I knew they had abandoned me to the Wild Hunt.” He swallowed painfully. “I thought it was because they feared Gwyn and the vengeance of the Hunt. Not because they hated and despised me.”

“It wasn’t hate,” said Julian. “It was fear.”

“They said that we couldn’t look for you,” said Ty. He had taken one of his toys out of his pocket: a length of cord that he often ran through and under his fingers, bending and shaping it into figure eights. “That it was forbidden. It’s forbidden to visit Helen, too.”

Mark looked toward Julian, and his eyes were dark with anger, black and bronze. “Did you ever even try?”

“I won’t fight with you, Mark,” Julian said. The side of his mouth was twitching; it was something that happened only when he was deeply upset, and something, Emma guessed, that only she would notice.

“You won’t fight for me either,” Mark said. “That much is clear.” He glanced around the room. “I have come back to a world where I am not wanted, it seems,” he said, and slammed his way out of the library.