‘Do you take yours black?’ Pierce asked, offering me the milk. ‘Anyway. I was trying to think of other strategies. I thought I might try to shut down the psychogeography business in London once and for all. If I could write the ultimate psychogeographical index of London, gathering up and pinning down every mystical wrinkle, backwoods fact and obscure snip of folklore – a psychopedia of London – I could make the field obsolete. A Key to all Mythologies, like Casaubon in Middlemarch. And that’s the problem: the Casaubon Complex. It can’t be done. Not that London is somehow special, although it is very big and very old. But I could take a lifetime doing it and it still wouldn’t be finished. And what if I did finish it? A 5,000-page, multi-volume slab of what amounts to pub trivia; it would only fuel the fire. It would be on the Zaha Hadid coffee table in every penthouse in Docklands.’

He turned in his chair, away from me, towards the map, shoulders hunched, tense. ‘I squandered months, years.’

‘Is that what you’ve been doing since Night Traffic?’ I asked. I couldn’t help but feel disappointed. As secret projects went, it was not what I expected, not very exciting, and not even going to happen.

‘No, no,’ Pierce said, looking back at me, scowling. ‘I stopped working on that ages ago. When Quin got involved. He came to one of my readings, for Murder Boards. Said he was a fan. Said he was working on a new mapping system for London, part map, part social network – this was Tamesis, but at the time they had a code name for it, Canny Valley. He wanted my input. Obviously, mapping, maps, I told him about my map. He loved it. He had this place swarming with Bunk staff, photographing, scanning, measuring, indexing, getting everything. Not just the psychopedia, some of the stuff I had gathered for Murder Boards too. Quin in the middle, sitting where you are now, laptop on his lap, issuing commands. Commands I didn’t even understand. Then they left. And they didn’t leave a trace. It was like Burning Man. But they did leave me a toy.’

Pierce leaped out of his seat, and the abrupt movement made me jump. He went over to one of the filing cabinets, opened the top drawer, and took out a tablet computer.

‘An interface for updating the map,’ Pierce said, returning to his armchair. He had switched on the tablet and handed it to me. ‘If I added anything, they wanted to know it.’