He wonders, a little too late, if he has been followed or photographed. He steps into a pub, clutching his picture under his arm. With one hand he sips a lemonade – ordinary bloke at bar with £30m. Matisse under arm – and then leaves by another door which leads directly into a mews. He’s passing, he realises, the front door of the billionaire widow of the first man to invent perforated toilet paper. She’s one of their clients and he’s dined there once or twice. His father never grasped the idea that great wealth corrupts. Or tends to corruption. His father regarded his wealth as a confirmation of his unique qualities, qualities which selective breeding of the privileged had produced. It is the updated version of the Victorian idea that the English gentleman was the outcome – even Darwin seemed to believe this – of years of evolution, fostered by rugby, cold showers, beating, poor food and study of the classics.

From the mews, standing in a doorway, he calls Kasimir.

‘I’m bringing over the picture.’

‘Right, we will be ready Mr Trevelyan-Tubal.’

‘I’m walking down Dover Street, I’ll be there in a few minutes.’

‘I can’t wait to see it.’

Kasimir is himself a kind of banker. He knows how to read the signs of financial distress and how to maintain decorum. He never utters a single word about his clients, the guilty and shifty sellers and the brash and eager buyers. He knows that their positions can change fast. The art market is inherently unstable because so many of the buyers are megalomaniacs and megalomaniacs believe their own judgements, which don’t necessarily apply to art.

Kasimir is waiting. If he is surprised to find that Julian has come on foot, he doesn’t comment. He wears a charcoal suit with exceptionally broad pinstripes that hug his elderly but slim shape fondly. His collar is high and cut dramatically away like the wings of a hovering kestrel. It is hovering over a pale-blue silk tie. His hair is slightly orange, thinning at the temples in a Middle Eastern way. Nobody knows precisely where Kasimir’s family came from; it is said they were big in the Ottoman Empire until the First World War. And indeed Kasimir retains a grave, Ottoman courtesy. His only weakness is young men. He has a small troupe, an ever-changing cast, which accompanies him to galleries and shows. But even they are tight-lipped, the Trappists of the catamite world.

‘Mr Trevelyan-Tubal, how marvellous to see you. Come, come into my office.’

Through the reception – paintings and tapestries on the walls in rich profusion – he shows Julian into his sanctum, which has a reinforced door.

‘May I?’

‘Of course.’

With a small blade and exquisite delicacy, as if he were slicing a persimmon, he removes the wrapping.

‘What a picture,’ he says, ‘what a wonderful picture.’