“The ninth circle of Hell is cold,” Tessa said automatically.

Will stared at her. “What?”

“In the Inferno,” she told him. “Hell is cold. It’s covered in ice.”

He stared at her for another long moment, the corners of his mouth twitching, then held out his hand. “Give me the witchlight.” At her blank expression he made an impatient noise. “The stone. Give me the stone.”

The moment his hand closed about the stone, light blazed up from it again, raying out through his fingers. For the first time Tessa saw that he had a design on the back of his hand, drawn there as if in black ink. It looked like an open eye. “As for the temperature of Hell, Miss Gray,” he said, “let me give you a piece of advice. The handsome young fellow who’s trying to rescue you from a hideous fate is never wrong. Not even if he says the sky is purple and made of hedgehogs.”

He really is mad, Tessa thought, but didn’t say so; she was too alarmed by the fact that he had started toward the wide double doors of the Dark Sisters’ chambers.

“No!” She caught at his arm, pulling him back. “Not that way. There’s no way out. It’s a dead end.”

“Correcting me again, I see.” Will turned and strode the other way, toward the shadowy corridor Tessa had always feared. Swallowing hard, she followed him.

The corridor narrowed as they went along it, the walls pressing in on either side. The heat was even more intense here, making Tessa’s hair spring into curls and paste itself to her temples and neck. The air felt thick and was hard to breathe. For a while they walked in silence, until Tessa could stand it no longer. She had to ask, even though she knew the answer would be no.

“Mr. Herondale,” she said, “did my brother send you to find me?”

She half-feared he’d make some mad comment in response, but he simply looked at her curiously. “Never heard of your brother,” he said, and she felt the dull ache of disappointment gnaw at her heart. She’d known Nate couldn’t have sent him—he’d have known her name, then, wouldn’t he?—but it still hurt. “And outside of the past ten minutes, Miss Gray, I’d never heard of you, either. I’ve been following the trail of a dead girl for near on two months. She was murdered, left in an alley to bleed to death. She’d been running from … something.” The corridor had reached a forking point, and after a pause Will headed to the left. “There was a dagger beside her, covered in her blood. It had a symbol on it. Two snakes, swallowing each other’s tails.”

Tessa felt a jolt. Left in an alley to bleed to death. There was a dagger beside her. Surely the body had been Emma’s. “That’s the same symbol that’s on the side of the Dark Sisters’ carriage—That’s what I call them, Mrs. Dark and Mrs. Black, I mean—”

“You’re not the only one who calls them that; the other Downworlders do the same,” said Will. “I discovered that fact while investigating the symbol. I must have carried that knife through a hundred Downworld haunts, searching for someone who might recognize it. I offered a reward for information. Eventually the name of the Dark Sisters came to my ears.”

“Downworld?” Tessa echoed, puzzled. “Is that a place in London?”

“Never mind that,” said Will. “I’m boasting of my investigative skills, and I would prefer to do it without interruption. Where was I?”

“The dagger—” Tessa broke off as a voice echoed down the corridor, high and sweet and unmistakable.

“Miss Gray.” Mrs. Dark’s voice. It seemed to drift between the walls like coiling smoke. “Oh, Miss Graaaay. Where are you?”

Tessa froze. “Oh, God, they’ve caught up with—”

Will seized her wrist again, and they were off running, the witchlight in his other hand throwing a wild pattern of shadows and light against the stone walls as they hurtled down the twisting corridor. The floor sloped down, the stones underfoot growing gradually more slick and damp as the air around them grew hotter and hotter. It was as if they were racing down into Hell itself as the voices of the Dark Sisters echoed off the walls. “Miss Graaaaaay! We shan’t let you run, you know. We shan’t let you hide! We’ll find you, poppet. You know we will.”

Will and Tessa careened around a corner, and came up short—the corridor ended at a pair of high metal doors. Releasing Tessa, Will flung himself against them. They burst open and he tumbled inside, followed by Tessa, who spun to slam them shut behind her. The weight of them was almost too much for her to manage, and she had to throw her back against them to force them, finally, closed.

The only illumination in the room was Will’s glowing stone, its light sunk down now to an ember between his fingers. It lit him in the darkness, like limelight on a stage, as he reached around her to slam the bolt home on the door. The bolt was heavy and flaking with rust, and, standing as close to him as she was, she could feel the tension in his body as he dragged it home and let it fall into place.

“Miss Gray?” He was leaning against her, her back against the closed doors. She could feel the driving rhythm of his heart—or was it her heart? The odd white illumination cast by the stone shimmered against the sharp angle of his cheeks, the faint sheen of sweat on his collarbones. There were marks there, too, she saw, rising from the unbuttoned collar of his shirt—like the mark on his hand, thick and black, as if someone had inked designs onto his skin.

“Where are we?” she whispered. “Are we safe?”

Without answering he drew away, raising his right hand. As he lifted it, the light blazed up higher, illuminating the room.

They were in a sort of cell, though it was very large. The walls, floor, and ceiling were stone, sloping down to a large drain in the middle of the floor. There was only one window, very high up in the wall. There were no doors save the ones they had come through. But none of that was what made Tessa draw in her breath.

The place was a slaughterhouse. There were long wooden tables running the length of the room. Bodies lay on one of them—human bodies, stripped and pale. Each had a black incision in the shape of a Y marking its chest, and each head dangled back over the edge of the table, the hair of the women sweeping the floor like brooms. On the center table were piles of bloodstained knives and machinery—copper cogs and brass gears and sharp-toothed silver hacksaws.

Tessa crammed a hand into her mouth, stifling a scream. She tasted blood as she bit down on her own fingers. Will didn’t seem to notice; he was white-faced as he looked around, mouthing something under his breath that Tessa couldn’t make out.

There was a crashing noise and the metal doors shuddered, as if something heavy had flung itself against them. Tessa lowered her bleeding hand and cried out, “Mr. Herondale!”

He turned, as the doors shuddered again. A voice echoed from the other side of them: “Miss Gray! Come out now, and we won’t hurt you!”

“They’re lying,” Tessa said quickly.

“Oh, do you really think so?” Having packed as much sarcasm into the question as was humanly possible, Will pocketed his glowing witchlight and leaped onto the center table, the one covered in bloodied machinery. He bent down and caught up a heavy-looking brass cog, and weighed it in his hand. With a grunt of effort he hurled it toward the high window; the glass shattered, and Will raised his voice. “Henry! Some assistance, please! Henry!”

“Who’s Henry?” Tessa demanded, but at that moment the doors shuddered a third time, and thin cracks appeared in the metal. Clearly, they weren’t going to hold much longer. Tessa dashed to the table and seized a weapon, almost at random—this one was a ragged-toothed metal hacksaw, the kind butchers used to cut through bone. She whirled around, clutching it, as the doors burst open.

The Dark Sisters stood in the doorway—Mrs. Dark, as tall and bony as a rake in her shining lime green gown, and Mrs. Black, red-faced, her eyes narrowed to slits. A bright corona of blue sparks surrounded them, like tiny fireworks. Their gazes slid over Will—who, still standing on the table, had drawn one of his icy blades from his belt—and came to rest on Tessa. Mrs. Black’s mouth, a red slash in her pale face, stretched into a grin. “Little Miss Gray,” she said. “You ought to know better than to run. We told you what would happen if you ran again… .”

“Then do it! Whip me bloody. Kill me. I don’t care!” Tessa shouted, and was gratified to see that the Dark Sisters looked at least a little taken aback by her outburst; she’d been too terrified to raise her voice to them before. “I won’t let you give me to the Magister! I’d rather die!”

“What an unexpectedly sharp tongue you have, Miss Gray, my dear,” said Mrs. Black. With great deliberation she reached to draw the glove from her right hand, and for the first time, Tessa saw her bare hand. The skin was gray and thick, like an elephant’s hide, her nails long dark talons. They looked as sharp as knives. Mrs. Black gave Tessa a fixed grin. “Perhaps if we cut it out of your head, you’d learn to mind your manners.”

She moved toward Tessa—and was blocked by Will leaping down from the table to put himself between them. “Malik,” he said, and his ice-white blade blazed up like a star.

“Get out of my way, little Nephilim warrior,” said Mrs. Black. “And take your seraph blades with you. This is not your battle.”

“You’re wrong about that.” Will narrowed his eyes. “I’ve heard some things about you, my lady. Whispers that run through Downworld like a river of black poison. I’ve been told you and your sister will pay handsomely for the bodies of dead humans, and you don’t much mind how they get that way.”

“Such a fuss over a few mundanes.” Mrs. Dark chuckled and moved to stand beside her sister, so that Will, with his blazing sword, was between Tessa and both ladies. “We have no quarrel with you, Shadowhunter, unless you choose to pick one. You have invaded our territory and broken Covenant Law in doing so. We could report you to the Clave—”

“While the Clave disapproves of trespassers, oddly they take an even darker view of beheading and skinning people. They’re peculiar that way,” Will said.

“People?” Mrs. Dark spat. “Mundanes. You care no more about them than we do.” She looked toward Tessa then. “Has he told you what he really is? He isn’t human—”

“You’re one to talk,” Tessa said in a trembling voice.

“And has she told you what she is?” Mrs. Black demanded of Will. “About her talent? What she can do?”

“If I were to venture a guess,” Will replied, “I would say it has something to do with the Magister.”

Mrs. Dark looked suspicious. “You know of the Magister?” She glanced at Tessa. “Ah, I see. Only what she has told you. The Magister, little boy angel, is more dangerous than you could ever imagine. And he has waited a long time for someone with Tessa’s ability. You might even say he is the one who caused her to be born—”