At the end the corridor suddenly opened up to a large, high-ceilinged chamber that had been built for storage or cellaring food. Alec waved his witchlight around, revealing rows of unlit candles all over the room.

“Well, that’s easy enough,” said Magnus, and with a snap of his fingers all the candles kindled, bringing bright warm light into the room.

This was definitely a former cellar. On the far end was a shoddy, rickety altar that cavemen might have erected to worship a fire god. Two wooden columns flanked a large stone block cut into a perfect cube on a raised platform.

On the left wall was a table that looked like cheap plastic lawn furniture covered with incense and prayer beads and other generic-looking knickknacks that someone could buy at a yoga studio.

“Oh my God, my cult is so low-rent,” moaned Magnus. “I am deeply shamed. I am disowning my followers for being evil and having no panache.”

“But it’s not your cult,” Alec said distractedly. He walked over to the side table and ran his finger along its surface. “There’s a lot of dust. This place hasn’t been used in a while.”

“I’m joking,” said Magnus. “Whistling in the dark.” He glanced at the empty corner of the room, where a tree root had pushed its way inside from between two stones. He walked up to the vine and yanked it. Nothing happened. He cast some detection magic over the corner. Still nothing.

“There has to be more,” said Shinyun. “Where are the signs of terrible rituals being done? Where is the blood on the walls?”

Alec picked up a small statuette and shook his head.

“There’s a manufacturer’s sticker here. Someone bought this in a souvenir shop. If this thing is magical, then I’m the Angel Raziel.”

“The Shadowhunters really wouldn’t approve of me dating the Angel Raziel,” said Magnus.

“But they’d have to be nice to you,” Alec said, brandishing the statuette, “or I would smite them.”

“Can you never be serious?” asked Shinyun. She strode toward the makeshift altar, then suddenly tripped and sprawled onto the ground. There was a silence during which nobody laughed. Magnus and Alec stood identically bug-eyed. After a long moment Shinyun snapped from the ground, “Well, someone look and see what I tripped over, at least.”

As she sat up and brushed the dust from her clothes, Magnus walked over and knelt down. Set in the earth floor before the altar was a tiny stone statue of a goat. Magnus knelt down and murmured into the statue’s ear the password Johnny Rook had given him. “Asmodeus.”

“What?” Alec said.

Magnus had deliberately spoken more softly than even a Shadowhunter could hear. He avoided Alec’s eyes.

The sound of grinding stone echoed throughout the room, drowning out whatever moment had been brewing between the two of them. The stone cube on the altar unfolded like a flower. It lifted from the altar and floated to the wall behind, where it embedded itself into the stone there. The platform the cube had been resting on crumbled into powder. Red-gold light appeared around the rosette that the stone cube had become, tracing the outline of a door.

The glowing outline solidified into an intricately detailed gold-plated door with a large oval mirror in the center.

Magnus walked up to the new door and studied it. He looked at his reflection in the mirror and then back at the rickety wooden door up front. “This is more what I was expecting,” he said, and reached for the handle.

Both Alec and Shinyun were there in a flash, trying to prevent Magnus from entering first. Alec and Magnus’s essential desire to avoid conflict meant that Shinyun won, nudging the two of them out of the way and pushing the door open. It swung open easily, revealing a long corridor with a low ceiling. A rush of stale air blew past them. A row of torches along the wall sparked and lit one by one down the line.

The corridor curved around several bends, making what was no more than a five-minute walk seem endless. Magnus had no sense at this point where they were in relation to the palazzo or even the city of Venice. If it were me, and it might have been, he thought, I would just plonk the whole thing in the middle of the lagoon somewhere. Ahead of him, Shinyun gasped as the passageway opened into what Magnus desperately hoped was the last secret chamber to find. Just the thought of the walk back made him want to lie down and take a nap.

He and Alec followed Shinyun into the chamber, and he understood why Shinyun had gasped. The space was huge, its decor the result of a church and a nightclub having gotten together for a wild night.

There were two sections of golden pews along each side of the room, and tiles flashing like jewels lined the walls beside them. At the far end of the room was a large painting of a handsome man with a long, bony face and sharp features. He would have almost passed for human if it were not for his jagged teeth. The only decoration he wore was a crown of barbed wire.

In front of the painting was a stone altar—a much more impressive one—in the center of a giant pentagram. Small grooves were carved into the stone slab, leading downward out from the four corners of the altar to the points of the star below. The entire space was mottled over with dark red stains whose shade varied, but were all of a piece.

“See?” said Shinyun triumphantly. “Blood on the walls. That’s how you know it’s the real one.”

Alec pointed to the left, puzzlement flashing on his face. “Why is there a fully stocked bar next to the sacrificial altar?”