Samuel looked at the stone for a long time. ‘You’ll excuse me,’ he said, ‘but I’ve never seen a diamond like this before, and I never will again. I want to make sure that I remember this moment. So, Barney Blitz was your father, was he? You could knock me down with a feather.’

‘The point is,’ said Peter, ‘where can I go with such a diamond?’

Samuel laid the diamond carefully back on his workbench. ‘There’s only one man that I know of. Garth Steinman. I don’t know whether you’ve ever heard of him or not, but he’s a dealer in unusual and speciality jewels only. Quite an eccentric, but a very rich eccentric. He acquired the Montfort emeralds for the late Queen. He’s a friend of the Rothschilds, and of J. P. Morgan. He has a house in St John’s Wood, although he may not be there now. He winters in Italy, and spends his summers in Switzerland.’

Peter took back the diamond and slipped it into the drawstring sachet. ‘I can only try. Do you think you can find me his address?’

‘My dear chap,’ said Samuel, ‘for the sake of a diamond like that, I’ll even take you there.’

Samuel closed the jeweller’s shop early, and the two of them hailed a hansom from the corner of Gray’s Inn Road. The rush-hour traffic was easing off now, and the early evening sunlight filled the interior of the cab with gilded motes of dust. Neither of the friends spoke very much as they turned westwards towards Euston station. Peter felt as if the whole of his world had altered, as if he were now involved in a theatrical performance of his own life, rather than the real thing.

It took them a little over twenty minutes to reach the quiet sidestreet in St John’s Wood where Garth Steinman’s residence stood. The Steinman house was only one of a whole row of huge, expensive mansions, each with a high wall and hedges. In those days, St John’s Wood, although it was only a mile or so north of Marylebone, was a quiet secluded village of its own, and the air was noticeably fresher than it had been in Holborn. Peter and Samuel alighted from the cab and paid the cabbie 1s 3d, with 3d tip.

Samuel rang at the bell-pull on the gate. But it was almost five minutes before a gardener, who was trundling a wheelbarrow of dug-up daffodil bulbs, came past the front of the house and noticed them. A little while later, a footman in a green coat and stockings came out to enquire what they wanted.

‘Mr Steinman, if he’s at home,’ said Peter.

‘You have an appointment, sir?’

‘I have something better than an appointment.’

‘Sir?’

‘I have the largest diamond he’s ever seen in his life.’

The footman said, ‘I’m afraid Mr Steinman is seeing nobody today. He has a headache.’