It was your basic dingy basement flat. Despite the modern kitchen conversion and Habitat trim, the low ceiling and poor lighting made it seem pinched and mean. I glanced into the front room as we passed and saw that all the furniture had been neatly piled against the far wall. Heavy-duty power cables snaked out of the rooms and down the hallway. They were securely held down with gaffer tape and plastic safety bridges.

It got noticeably warmer the closer we got to the back door, so that by the time the girl held out her hand to accept our coats we were already half out of them. She took them into the back bedroom which had been filled with portable clothes racks – we even got tear-off raffle tickets as receipts.

‘You go out through the kitchen,’ said the girl.

We followed her instructions, opened the back door and stepped out into a crisp inexplicable autumn afternoon. The entire width and length of the back garden was filled with a scaffolding frame that rose until it was level with the roof of the house. Plank flooring was raised half a metre above the lawn. From there, ladders led upwards to ‘balconies’ constructed of scaffolding poles and more planking. The construct encompassed an entire tree and was enclosed in white plastic sheeting. Golden sunlight flooded down from above, from an HMI lighting balloon, I learnt later, which explained the cabling snaking up the scaffolding.

Trestle tables were ranged between the upright poles to form a line of makeshift booths along each side of the garden. I had a look at the first on the right, which sold books, antique hardbacks for the most part, individually wrapped in mylar and arranged face up in wooden trays. I picked up an eighteenth-century reprint of Méric Casaubon’s On Credulity and Incredulity in Things natural, civil and divine that looked very similar to the copy we had back at the Folly. Next to that I found another familiar book, a 1911 copy of Erasmus Wolfe’s Exotica, which was definitely hardcore ‘craft’ and judging from the stamp had been lifted from the Bodleian Library. I flicked through the book and memorised the security code to pass on to Professor Postmartin later. I replaced the book and smiled at the stallholder. He was a young man with ginger hair who appeared to be wearing a tweed suit that was twice as old as he was. He had pale blue eyes that flicked away nervously when I asked him whether he had a copy of the Principia.

‘Sorry,’ he said. ‘I’ve heard of it but I’ve never even seen a copy.’

I said that was a pity and turned away – he was lying and he’d made me and Lesley as the filth.

‘Nightingale was right,’ I said to Lesley. ‘This is a nazareth.’