I got back to town at five in the afternoon, the November day already as dark as midnight and London’s 180-minute rush hour starting to get mad. I sent Wren a text when I was on Piccadilly and she was waiting for me outside 27 Savile Row when I arrived. She got into the X5 with a triumphant smile.

‘If it wasn’t for me,’ she said, ‘you’d still be dicking about on Google. I’d go through Regent’s Park, if I were you. The traffic is always surprisingly light around the park.’

I took the park route and within fifteen minutes we were on the Finchley Road, the traffic heavy but moving steadily; and then it was thinning and the road was rising steeply towards the end of Heath Street as we climbed to the highest point of the city.

I realised that we were close to the meadow where Scout and I had let Stan off his lead and lost him. I had never noticed all the art galleries before. You drive out of Hampstead and they are the last thing you see, a cluster of them, all shapes and sizes, just before you are surrounded by the wild green expanse of the Heath.

As the car crawled higher, I saw that some of these galleries were high end, great lavish spaces with large, expensively lit canvases displayed in the window; other places were far more modest, local artists selling their work to a local clientele. The one we were looking for was little more than a darkened hole in the wall.

‘This is it,’ Wren said.

NEREUS

Fine Art

I slowed as we drove past and caught a glimpse of a tiny space behind wrought-iron railings glinting under the streetlights. A recycling bin was overturned, its contents spilled over the narrow pavement. Wren was already unclipping her seat belt as I crested the hill. I found a parking space behind Jack Straw’s Castle.

But when we walked back to the gallery we found that Nereus Fine Art was closed. Two small landscapes were displayed in the window. A wave of junk mail was washed up inside the glass door. BACK SOON lied a sign.

I stood back. It was a three-storey building: the small gallery had a basement flat below and a flat above. I leaned over the wrought-iron railings, looking down and then up. Both of the flats were in darkness. Broken glass crunched beneath my feet and the recycling bin looked as though it had been rifled through by a fox that had come down from the Heath. He had been out of luck. It was just beer bottles and empty pizza boxes.