The American girl took the stone from his fingers and turned it over and over. Then she looked at the Saint again.
'I know this much,' she said. 'It's a——'
'Look out!' yelled Monty.
He had seen the prince's hand move casually to his sleeve, as if in search of a handkerchief, and had thought nothing of it. Then the hand came out again with a jerk, and the knife that came with it went spinning across the desk in a vicious streak of silver. The Saint hurled himself sideways, and it skimmed past his neck and clattered against the wall. The prince flung himself after it like a madman, clawing at the Saint's gun.
Simon stood up and met him with a straight left that smashed blood out of the contorted face and set the man staggering back against his chair.
'Keep your gun in his ribs, Monty,' ordered the Saint crisply. 'This is getting interesting. What were you going to tell me, Miss Walden?'
The girl gave him back the stone.
'It's a piece of coloured glass,' she said.
2
Simon Templar subsided on to the desk as if his legs had given out under him. The room danced round him in a drunken tango. And once again he heard the dying jest of Josef Krauss ringing in his ears:
'The Ullsteinbach diamond is in America.' Nina Walden went on speaking without a glance at the prince. 'It was sold to Wilbur G. Tully, the straw hat millionaire, just before the war. The owners were hard up, and they had to raise money somehow: their treasurers wouldn't give them any more, so they raided the crown jewels. This imitation was made, and the real stone was sold to Tully under a vow of secrecy. He keeps it in his private collection. I don't think any living person knows the story besides Tully and myself. But my grandfather made the imitation. I've known about it for years, and I've been saving the scoop for a good occasion. The Archduke Michel did that when he was sowing wild oats in his fifties—
'Great God in Heaven!'
The Saint leapt up again. He understood. The mystery was solved in a flash that almost blinded him. He cursed himself for not having thought of it before. And he was half laughing at the same time, shaking with the sublime perfection of the truth.
'Let me get this straight!' he gasped. 'It wasn't the other crown jewels that Rudolf gave a damn about. They just happened to be among the spoils. What he wanted was the Ullsteinbach blue diamond. And he didn't want it because it was valuable, but because it wasn't—because it was literally priceless! He couldn't let the jewels come into any ordinary market, because someone would certainly have discovered the fraud, and the whole deception would have been shown up from the beginning. The old Archduke would probably have been booted off the throne, and Rudolf would have gone with him. He had to let Josef Krauss pinch the jewels, and then take them off Josef. Josef had discovered the secret when he handled the stones, so he had to go. And then I got hold of them by a fluke, and I might have discovered it—so I was a marked man. And everyone with me was in the same boat. Hell! ...'
The Saint flung out his arms.
'I said it wasn't ordinary boodle—and it isn't! It's the most priceless collection of boodle that's ever been knocked off! There were men dying and being tortured for it—mail vans broken—policemen sweating—thrones tottering—and all because the star turn of it wasn't worth more than an empty beer bottle! My God—why didn't I know that joke hours ago? Why wasn't I told till now?'
He hugged Nina Walden weakly.
Monty swallowed. He didn't know what to say. He realized dimly that he had just heard the unravelling of the most amazing story he was ever likely to hear, but it was all too crushingly simple. For the moment his brain refused to absorb the elementary enormity of it.
In the same daze he saw Simon Templar pick up the glittering blue crystal from the carpet where he had dropped it and advance solemnly towards the Crown Prince. And the Saint's voice spoke uncertainly.
'Rudolf—my cherub—you may have it as the souvenir I promised
