I fumbled in the dark for my torch, turned it on, and quickly got it trained on the foyer. Other beams of light stabbed out of the darkness. Everyone else was as keen as I was to make sure that whatever came back through the foyer was somebody we knew.

The rope was slack in my hands.

“Inspector,” I called. “Are you okay?”

The rope went taut suddenly and I had to brace not to be pulled over.

“I’m quite all right,” said Nightingale. “Thank you for asking.”

I coiled up the rope as he returned. His face was pale in the torchlight. I asked him if he was all right again, but he just gave me a strange grimace as if remembering some serious pain. Then he unclipped the rope and went over to talk to the head forensics guy. Whatever he said, the forensics guy wasn’t happy. When Nightingale had finished, the man called over two of the younger-looking techs and told them something in a low voice.

One of the techs, a young man with Trotsky specs and an emo fringe, protested. But his boss shut him down and sent him and his mate packing up the stairs.

Nightingale came over and asked the Somali ninja girl to run upstairs and tell Stephanopoulis that the building was secure, but that we hadn’t found any suspects.

“A demon trap?” I asked.

“That’s just a nickname,” said Nightingale. “It’s a booby trap. I suppose you could call it a magical land mine. I haven’t seen one of those since 1946.”

“Shouldn’t I know about these things?” I said.

“The list of things you need to know about, Peter, is extraordinarily long,” said Nightingale. “And I have no doubt that even you will eventually cover them all. But there’s no point learning about demon traps until you’ve studied basic enchantment.” He held up his cane to show that the silver top was blackened and melted in places. Enchantment, I knew from my reading, was the process by which inanimate objects are imbued with magical qualities.

Nightingale examined the cane ruefully. “Although I may be demonstrating how it’s done in the next couple of months,” he said. “That being the case, we may as well provide you with a training staff while we’re at it.”

“The demon trap,” I said. “Did you recognize the signature?”

“The signare?” he asked. “Not the individual, but I think I know who trained the vicious little so-and-so.”

“Geoffrey Wheatcroft?” I asked.

“The very same.”

“Could he have been the original magician?”

“That’s something we’re going to have to look into,” said Nightingale.

“He’d have to have schlepped back and forth between here and Oxford,” I said. “If he was doing that, then he must have had an assistant.”

“One of his pupils?”

“Who might have gone on to be our new magician,” I said.

“This is all terribly speculative,” he said. “We need to find the assistant.”