Marie Curie had been a small white rat Christopher had kept in the room at the Devil Tavern and fed on bread and chicken bones. Marie had been friendly enough to rest on Lucie’s shoulder and nuzzle at her hair. Eventually Marie had died of natural causes and been buried with pomp and circumstance in Matthew’s back garden.

“But I don’t know if we ought to feel sorry for Grace,” said Lucie. “She broke James’s heart.”

“For someone with a broken heart, he seems in remarkably fine fettle,” said Thomas. “Honestly, he actually seems more cheerful.”

Lucie could not deny that this was true. “Still,” she said. “It is the principle of the thing.”

They reached the greenhouse, a long structure of glass and wood. Long ago it had provided the Lightwood family with pineapples and grapes in winter. Now there were holes smashed into the glass walls, and the once-clean windows were smeared and dark.

A massive padlock hung on the door. Lucie started to reach for her stele, but Thomas put a hand on her wrist. “I can go around the back,” he said. “There ought to be a small shed there with an entrance into the greenhouse. They would have needed to heat the place by hypocaust.”

“I have no idea what you mean,” said Lucie. “But I suspect you know this because of all the hours you’ve spent listening to Christopher in the lab. Certainly, by all means, let us crawl into a dark and spider-infested shed.”

“It isn’t spiders I’m worried about,” said Thomas. “And you won’t be doing any crawling. We need you out here as sentry. If you see any unusual activity, send up an alarm.”

“I hate being the watchman. Are you certain we need one?”

“Yes,” said Thomas, “because if one of us is going to be devoured by demonic tree roots, then the other one had better be around to get help, or at least grab the malos root and run for it.”

Lucie had to admit he had a point. “Go on, then.”

Thomas headed toward the back of the greenhouse. Lucie attempted to do as he had suggested for at least five minutes, but it was very dull. There was only so long one could pace back and forth in front of the door to a greenhouse before feeling like a goldfish swimming to and fro in its bowl. She was very nearly relieved to glimpse something out of the corner of her eye.

It looked like a spark of bright light, down toward the Italian gardens. She moved away from the greenhouse, narrowing her eyes. The light was pale in color and wavering against the twilight. A torch, perhaps?