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

"I demand pardon, my friend. Her hand concealed the part of it where the gap would have shown. To place a piece of silk in the door beforehand is child's play! Of course, as soon as Rolf read of the robbery, he arranged his own little comedy. And very well he played it!"

"What did you say to him?" I asked with lively curiosity.

"I said to him that Lady Yardly had told her husband all, that I was empowered to recover the jewel, and that if it were not immediately handed over proceedings would be taken. Also a few more little lies which occurred to me. He was as wax in my hands!"

I pondered the matter.

"It seems a little unfair on Mary Marvell. She has lost her diamond through no fault of her own."

"Bah!" said Poirot brutally. "She has a magnificent advertisement. That is all she cares for, that one!

Now the other, she is different. Bonne mère, très femme!"

"Yes," I said doubtfully, hardly sharing Poirot's views on femininity. "I suppose it was Rolf who sent her the duplicate letters."

"Pas du tout," said Poirot briskly. "She came by the advice of Mary Cavendish to seek my aid in her dilemma. Then she heard that Mary Marvell, whom she knew to be her enemy, had been here, and she changed her mind, jumping at a pretext that you, my friend, offered her. A very few questions sufficed to show me that you told her of the letters, not she you! She jumped at the chance your words offered."

"I don't believe it," I cried, stung.

"Si, si, mon ami, it is a pity that you study not the psychology. She told you that the letters were destroyed? Oh, la la, never does a woman destroy a letter if she can avoid it! Not even if it would be more prudent to do so!"

"It's all very well," I said, my anger rising, "but you've made a perfect fool of me! From beginning to end! No, it's all very well to try to explain it away afterwards. There really is a limit!"

"But you were so enjoying yourself, my friend. I had not the heart to shatter your illusions."

"It's no good. You've gone a bit too far this time."

"Mon Dieu! but how you enrage yourself for nothing, mon ami!"

"I'm fed up!" I went out, banging the door. Poirot had made an absolute laughing-stock of me. I decided he needed a sharp lesson. I would let some time elapse before I forgave him. He had encouraged me to make a perfect fool of myself!

THE TRAGEDY AT MARSDON MANOR

I had been called away from town for a few days, and on my return found Poirot in the act of strapping up his small valise.

"A la bonne heure, Hastings. I feared you would not have returned in time to accompany me."

"You are called away on a case, then?"