‘It’s difficult to tell in gaslight,’ he said. ‘But if it is a real diamond, it’s magnificent. A slight pinkish tinge to it, don’t you see? Very slight, but enough to make it a “fancy” diamond, and increase its value four to five times over, if you can find anyone to pay that sort of money.’

‘Then you think it’s genuine?’

‘My dear chap, I couldn’t tell you for certain. This is the whole illusion of the diamond business. Not even quite reputable dealers are capable of telling whether some diamonds are real diamonds or not. There are plenty of very capable fakes around these days: and if they’re mounted, they’re even harder to detect. Some tricksters set inferior diamonds in a fine gold or silver setting, you see, and paint the back of the gems so that they reflect more light. There was the famous rainbow necklace of the Romanoffs, for instance. George Kunz, an American gemologist, and a very sceptical fellow, discovered by scratching the backs of the diamonds with his finger-nail that they were nothing but second-rate stones with paint on them.’

‘But this stone isn’t mounted,’ said Peter.

‘No,’ replied Samuel. ‘But it could be topaz, or strass, which is high-density lead glass, or even quartz; although I doubt that it’s quartz, because it appears too brilliant.’

Peter was silent for a moment, watching his friend examine the stone through his loupe, but then he said, ‘I have to tell you something which may make you change your opinion.’

‘Well, do,’ said Samuel, ‘because if this is a real diamond, then you’re in the money for the rest of your life, and I’m not joking.’

‘The Reverend Ransome wasn’t my real father,’ said Peter. ‘I know that I always pretended he was, when I was at school, but that was only because I was embarrassed about it. My real father was Barney Blitz.’

Samuel put down the diamond and looked at his schoolfriend in astonishment. ‘Now, you’re really having me on toast. This is just a practical joke, isn’t it? You’re going to go back to all the fellows at Kennington and tell them how Samuel Kellogg thought a piece of glass from a Christmas cracker was worth millions of pounds.’

‘Samuel, I’m telling you the truth. I swear it. When my mother was in South Africa, she lived with Barney Blitz for years. He was my real father.’

‘Well, you could knock me down with a feather,’ said Samuel.

Peter pointed to the diamond. ‘That’s why I’m quite sure that the diamond is real. And that’s why I have to know where I can take it to sell it. I don’t want to be sold short. My father gave that stone to my mother so that my future would be secure. I wouldn’t want to let him down by giving it to the first diamond dealer I meet for only a quarter of what it’s worth.’