“This isn’t unusual.” Nightingale’s voice was low and reassuring. “You have to get the foundations of the art right or everything you build on top will be crooked, not to mention unstable. There are no shortcuts in wizardry, Peter. If there were, everyone would be doing it.”

Probably on Britain’s Got Talent, I thought, but you don’t say these things to Nightingale because he doesn’t have a sense of humor about the art and only used the telly for watching rugby.

I assumed the attentive look of the dutiful apprentice but Nightingale wasn’t fooled.

“Tell me about your dead musician,” he said.

I laid out the facts with emphasis on the intensity of the vestigia Dr. Walid and I had felt around the body.

“Did he feel it as strongly as you did?” asked Nightingale.

I shrugged. “It’s vestigia, boss,” I said. “It was strong enough for both of us to hear a melody. That’s got to be suspicious.”

“It’s suspicious,” he said and settled back down in his wheelchair with a frown. “But is it a crime?”

“The statute only says that you have to unlawfully kill someone under the Queen’s Peace with malice aforethought. It doesn’t say anything about how you do it.” I’d checked in Blackstone’s Police Manual before coming down for breakfast that morning.

“I’ll be interested to see the Crown Prosecution Service argue that in front of a jury,” he said. “In the first instance you’ll need to prove that he was killed by magic and then find out who was capable of doing it and making it look like natural causes.”

“Could you do it?” I asked.

Nightingale had to think about that. “I think so,” he said. “I’d have to spend a while in the library first. It would be a very powerful spell, and it’s possible that the music you’re hearing is a practitioner’s signare—his involuntary signature.” Because, just as the old telegraph operators could identify one another from the way each one tapped their key, so every practitioner casts a spell in a style unique to themselves.

“Do I have a signature?” I asked.

“Yes,” said Nightingale. “When you practice, things have an alarming tendency to catch fire.”

“Seriously, boss.”

“It’s too early for you to have a signare but another practitioner would certainly know that you were my apprentice,” said Nightingale. “Assuming he’d ever seen my work, of course.”

“Are there other practitioners out there?” I asked.

Nightingale shifted in his wheelchair. “There are some survivors from the prewar mob,” he said. “But apart from them, you and I are the last of the classically trained wizards. Or at least you will be if you ever concentrate long enough to be trained.”

“Could it have been one of these survivors?”

“Not if jazz was part of the signare.”