“So far,” said Stephanopoulis. The joys of dealing with the bereaved when they’re both victim and suspect—I was glad I wasn’t doing that bit of the investigation. The flat had only one bedroom, a pair of masculine suitcases pushed into the corner, a line of packing cases with fingerprint dust smeared on the lids. Stephanopoulis showed me where a pile of books had been carefully arranged on a plastic sheet by the bed.

“Have they been processed?” I asked.

Stephanopoulis said yes, but I put on gloves anyway. It’s good practice when handling evidence and I got a grunt of approval from the sergeant. I picked up the first book; it was old, a prewar hardback that had been carefully wrapped in white tissue paper. I opened it and read the title: Philosophiae Naturalis Principia Artes Magicis by Isaac Newton. I had a copy of the same edition on my desk, with a much bigger Latin dictionary sitting next to it.

“We saw this,” said Stephanopoulis. “And we thought of you.”

“Are there any more?” I asked.

“We left the box for you,” she said. “Just in case it was cursed or something.”

I hoped she was being sarcastic.

I inspected the book. Its cover was worn at the edges and warped with age. The edges of the pages had dents and smears from being handled. Whoever had owned this book hadn’t left it on a shelf; this had been used. On a hunch I turned to page 27 and saw, just where I’d stuck in a Post-it note with a question mark on it, was the word, written in faded pencil, quis? Somebody else couldn’t work out what the hell Isaac was going on about in the middle part of the introduction.