THE GENERAL public have a warped view of the speed at which an investigation proceeds. They like to imagine tense conversations going on behind the venetian blinds and unshaven, but ruggedly handsome, detectives working themselves with single-minded devotion into the bottle and marital breakdown. The truth is that at the end of the day, unless you’ve generated some sort of urgent lead, you go home and get on with the important things in life—like drinking and sleeping and, if you’re lucky, a relationship with the gender and sexual orientation of your choice. And I would have been doing at least one of those things the next morning if I hadn’t also been the last bleeding apprentice wizard in England. Which meant I spent my spare time learning magic, studying dead languages, and reading books like Essays on the Metaphysical by John “never saw a polysyllabic word he didn’t like” Cartwright.

And learning magic, of course—which is what makes the whole thing worthwhile.

This is a spell: Lux iactus scindere—say it quietly, say it loudly, say it with conviction in the middle of a thunderstorm while striking a dramatic pose—nothing will happen. That’s because the words are just labels for the forma that you make in your mind; lux to make the light and scindere to fix it in place. If you do this particular spell right it creates a light source in a fixed position. If you do it wrong it can burn a hole through a lab table.

“You know,” said Nightingale, “I don’t think I’ve ever seen that happen before.”

I gave the bench a last squirt with the CO2 extinguisher and bent down to see whether the floor under the table was still intact. There was a burn mark but luckily no crater.

“It keeps getting away from me,” I said.

Nightingale stood up out of his wheelchair and had a look for himself. He moved carefully and favored his right side. If he was still wearing bandages on his shoulder they were hidden under a crisp lilac shirt that had last been fashionable during the abdication crisis. Molly was busily feeding him up, but to me he still looked pale and thin. He caught me staring,

“I wish you and Molly would stop watching me like that,” he said. “I’m well on the road to recovery. I’ve been shot before, so I know what I’m talking about.”

“Shall I give it another go?”

“No,” said Nightingale. “The problem is obviously with scindere. I thought you’d progressed through that too swiftly. Tomorrow we’re going to start to relearn that forma and then once I’m certain of your mastery we’ll return to this spell.”

“Oh joy,” I said.