"How did you know?" he muttered.
Again, Jimmy was surprised. He had expected indignant denials and demands for proof, excited reiteration of the statement that the stones had cost twenty thousand pounds.
"How did I know?" he repeated. "If you mean what first made me suspect, I couldn't tell you. It might have been one of a score of things. A jeweler can't say exactly how he gets on the track of fake stones. He can feel them. He can almost smell them. I worked with a jeweler once. That's how I got my knowledge of jewels. But, if you mean, can I prove what I say about this necklace, that's easy. There's no deception. It's simple. See here. These stones are supposed to be diamonds. Well, the diamond is the hardest stone in existence. Nothing will scratch it. Now, I've got a little ruby, out of a college pin, which I know is genuine. By rights, then, that ruby ought not to have scratched these stones. You follow that? But it did. It scratched two of them, the only two I tried. If you like, I can continue the experiment. But there's no need. I can tell you right now what these stones are, I said they were paste, but that wasn't quite accurate. They're a stuff called white jargoon. It's a stuff that's very easily faked. You work it with the flame of a blow-pipe. You don't want a full description, I suppose? Anyway, what happens is that the blow-pipe sets it up like a tonic. Gives it increased specific gravity and a healthy complexion and all sorts of great things of that kind. Two minutes in the flame of a blow-pipe is like a week at the seashore to a bit of white jargoon. Are you satisfied? If it comes to that, I guess you can hardly be expected to be. Convinced is a better word. Are you convinced, or do you hanker after tests like polarized light and refracting liquids?"
Sir Thomas had staggered to a chair.
"So, that was how you knew!" he said.
"That was—" began Jimmy, when a sudden suspicion flashed across his mind. He scrutinized Sir Thomas' pallid face keenly.
"Did you know?" he asked.
He wondered that the possibility had not occurred to him earlier. This would account for much that had puzzled him in the other's reception of the news. He had supposed, vaguely, without troubling to go far into the probabilities of such a thing, that the necklace which Spike had brought to him had been substituted for the genuine diamonds by a thief. Such things happened frequently, he knew. But, remembering what Molly had told him of the care which Sir Thomas took of this particular necklace, and the frequency with which Lady Julia wore it, he did not see how such a substitution could have been effected. There had been no chance of anybody's obtaining access to these stones for the necessary length of time.
"By George, I believe you did!" he cried. "You must have! So, that's how it happened, is it? I don't wonder it was a shock when I said I knew about the necklace."
"Mr. Pitt!"