And smiling and talking, the amazing little man conducted the bewildered nobleman to the door. He returned gently rubbing his hands.

‘Poirot,’ I said. ‘Am I quite demented?’

‘No, mon ami, but you are, as always, in a mental fog.’

‘How did you get the diamond?’

‘From Mr Rolf.’

‘Rolf?’

‘Mais oui!’ The warning letters, the Chinaman, the article in Society Gossip, all sprang from the ingenious brain of Mr Rolf! The two diamonds, supposed to be so miraculously alike – bah! they did not exist. There was only one diamond, my friend! Originally in the Yardly collection, for three years it has been in the possession of Mr Rolf. He stole it this morning with the assistance of a touch of grease paint at the corner of each eye! Ah, I must see him on the film, he is indeed an artist, celui-là!’

‘But why should he steal his own diamond?’ I asked, puzzled.

‘For many reasons. To begin with, Lady Yardly was getting restive.’

‘Lady Yardly?’

‘You comprehend she was left much alone in California. Her husband was amusing himself elsewhere. Mr Rolf was handsome, he had an air about him of romance. But au fond, he is very businesslike, ce monsieur! He made love to Lady Yardly, and then he blackmailed her. I taxed the lady with the truth the other night, and she admitted it. She swore that she had only been indiscreet, and I believe her. But, undoubtedly, Rolf had letters of hers that could be twisted to bear a different interpretation. Terrified by the threat of a divorce, and the prospect of being separated from her children, she agreed to all he wished. She had no money of her own, and she was forced to permit him to substitute a paste replica for the real stone. The coincidence of the date of the appearance of “The Western Star” struck me at once. All goes well. Lord Yardly prepares to range himself – to settle down. And then comes the menace of the possible sale of the diamond. The substitution will be discovered. Without doubt she writes off frantically to Gregory Rolf who has just arrived in England. He soothes her by promising to arrange all – and prepares for a double robbery. In this way he will quiet the lady, who might conceivably tell all to her husband, an affair which would not suit our blackmailer at all, he will have £50,000 insurance money (aha, you had forgotten that!), and he will still have the diamond! At this point I put my fingers in the pie. The arrival of a diamond expert is announced. Lady Yardly, as I felt sure she would, immediately arranges a robbery – and does it very well too! But Hercule Poirot, he sees nothing but facts. What happens in actuality? The lady switches off the light, bangs the door, throws the necklace down the passage, and screams. She has already wrenched out the diamond with pliers upstairs –’

‘But we saw the necklace round her neck!’ I objected.