“I feared your parents would not have considered it the kind of tale suitable for a young lady’s ears,” said Jesse. “I see that was an idle concern.”

“They tell it every Christmas,” said Lucie smugly.

Jesse stood up. Lucie could not help but glance at the mirror over the vanity, where she could see the reflection of her own face, but not Jesse. A girl in an empty room, talking to herself. “Grandfather Benedict dabbled in a great deal of black magic,” he said. “And his relationship with demons—” He shuddered. “When he died, he left a Cerberus demon behind in the greenhouse. Its mandate is to protect our family.”

“The demon James saw in the greenhouse? But he killed it. And when the Enclave searched the grounds, they found nothing.”

“The Cerberus had been bred with a certain demonic plant,” said Jesse. “When slain, it drops pods that at first look harmless. After some hours, they hatch and become new Cerberus demons. By now they would be full grown.”

Lucie felt a chill. “What do you fear?”

“Grace left the house without my mother’s knowledge—indeed, against her express orders. The newborn Cerberus demons would have sensed it. My grandfather instilled them with the mandate to protect our family. They will go forth to find Grace and retrieve her,” said Jesse.

“But how can you be sure? Why would the new demons inherit the mandate of the old?”

“I read it in my grandfather’s papers,” Jesse said. “He hoped to create an obedient demon that would give birth to new demons when slain—ones that would remember all their progenitor knew. Believe me, I never thought his plan would actually work. Grandfather was mad as a hatter. But by the time I became aware of what was going on, it was too late.”

“But…,” Lucie spluttered. “Will they harm Grace?”

“No. They regard her as a Blackthorn. But if Herondale—if your brother is with her, they will regard him as an enemy. He killed their progenitor in the greenhouse. They will attack him, and it will be no easy task to fend off a group of Cerberus demons alone.”

Not only would James be alone, Lucie was not even sure he was armed. “What does your mother know of this? Surely she could not have wanted a demon on her property—”

“My mother resents Shadowhunters, and not without reason. I think she has always felt protected by the presence of the Cerberus in the greenhouse.” Jesse sighed. “To be honest, I am not even sure she knows about the new demons. I only worked out what had happened when I saw them leaving the manor, and as a ghost, I could not stop them.” His voice was full of frustration. “I have not even been able to find my mother to warn her what is going on.”