I hauled my rucksack and two suitcases up to the landing. I pressed the brass doorbell but I couldn’t hear it ring through the thick doors. After a moment, they opened on their own. It might have been the traffic noise, but I swear I didn’t hear a motor or any kind of mechanism at all. Toby whined and hid behind my legs.

‘That’s not creepy,’ I said. ‘Not even in the slightest.’

I pulled my suitcase through the doors.

The entrance lobby had a mosaic floor in the Roman manner and a wooden and glass booth that, while in no way resembling a ticket booth, indicated that there was an inside and an outside to the building, and that one had better have permission if one wanted to proceed inside. Whatever this place was, it certainly wasn’t Nightingale’s private residence.

Beyond the booth, flanked by two neoclassical pillars, was a marble statue of a man dressed in an academic gown and breeches. He cradled a mighty tome in one arm and a sextant in the other. His square face held an expression of implacable curiosity, and I knew his name even before I saw the plinth, which read:

Nature and nature’s laws lay hid in night;

God said ‘Let Newton be’ and all was light.

Nightingale was waiting for me by the statue. ‘Welcome to the Folly,’ he said, ‘the official home of English magic since 1775.’

‘And your patron saint is Sir Isaac Newton?’ I asked.

Nightingale grinned. ‘He was our founder, and the first man to systemise the practice of magic.’

‘I was taught that he invented modern science,’ I said.

‘He did both,’ said Nightingale. ‘That’s the nature of genius.’

Nightingale took me through a door into a rectangular atrium that dominated the centre of the building. Above me there were two rows of balconies, and an iron and glass Victorian dome formed the roof. Toby’s claws clicked on a floor of polished cream-coloured marble. It was very quiet, and for all that the place was spotless I got a strong sense of abandonment.

‘Through there is the big dining room which we don’t use any more, the lounge and smoking room, which we also don’t use.’ Nightingale pointed to doors on the other side of the atrium. ‘General library, lecture hall. Downstairs are the kitchens, sculleries and wine cellar. The back stairs, which are actually at the front, are over there. Coach house and mews are through the rear doors.’

‘How many people live here?’ I asked.

‘Just the two of us. And Molly,’ said Nightingale.