“You’re a cruel man, Constable Grant,” said Postmartin. “No doubt you shall go far. The actual words, as you surmised, are irrelevant, but if the page numbers are arranged as a single alphanumeric string they form a unique identification number. Which we can enter into our venerable friend here and voilà …”

The PCW’s screen displayed a page of ugly green text, title, author, publisher, shelving notation, and a short list of the people who’d borrowed the book. The last person listed was Geoffrey Wheatcroft, who’d signed it out in July 1941 and never returned it.

“Oh,” said Postmartin in surprise. “Geoffrey Wheatcroft? Hardly what I’d call a nefarious fellow. Not your criminal type at all, is he, Thomas?”

“You know him?”

“I knew him,” said Postmartin. “He died last year—we were both at the funeral, although Thomas had to come as his own son to allay suspicions.”

“It was two years ago,” said Nightingale.

“Goodness, was it?” asked Postmartin. “Not a very good turnout if I remember.”

“Was he an active practitioner?” I asked.

“No,” said Nightingale. “He got his staff in 1939, wasn’t considered a wizard of the first rank, gave it up after the war and took up a position at Magdalen.”

“Teaching theology of all things,” said Postmartin.

“Magdalen College?” I asked.

“Yes,” said Nightingale suddenly thinking.

I got there first. “The same college as Jason Dunlop.”

NIGHTINGALE WANTED to head straight for Magdalen but Postmartin suggested a spot of lunch at the Eagle and Child. I thought a sit-down was a good idea because Nightingale was favoring his left side again and looking a bit peaky, to be honest. Nightingale compromised by suggesting that we should meet at the pub after visiting the college. Postmartin suggested that I go with him so that he could fill me in on a few things on the way.

“If you think that’s really necessary,” said Nightingale before I could object.

“I believe it is,” said Postmartin.

“I see,” said Nightingale. “Well, if you feel that’s best …”

Postmartin said he thought it was capital and so we accompanied him back to the car where I introduced him to Toby, who exited the vehicle in a cloud of smell. I suggested that Nightingale take the Jag—that way we’d drive back from the pub and he, at least, wouldn’t be walking.

“So this is the famous ghost-hunting dog,” he said.

“I didn’t know he was famous,” I said.

Postmartin led me down an alleyway so authentically late medieval that it still had a stone culver running down the middle to act as a sewer. “Not that it’s used for its original function,” said Postmartin.

It was busy with students and tourists all doing their best to ignore the cyclists who tried to mow down both with gay abandon.

I asked Postmartin what role he played in the intricate network of mostly unwritten agreements that constituted English magical law enforcement.