I was just getting into bed when it came to me. Hit me bang between the eyes. If Mrs. Luttrell had been killed, it would have been a case like those other cases. Colonel Luttrell would, apparently, have killed his wife. It would have been accounted an accident, yet at the same time nobody would have been sure that it was an accident, or whether it had been done on purpose. Insufficient evidence to show it as murder, but quite enough evidence for murder to be suspected. But that meant - that meant -

What did it mean?

It meant - if anything at all was to make sense - that it was not Colonel Luttrell who shot Mrs. Luttrell, but X.

And that was clearly impossible. I had seen the whole thing. It was Colonel Luttrell who had fired the shot. No other shot had been fired. Unless - But surely that would be impossible. No, perhaps not impossible - merely highly improbable. But possible, yes ... Supposing that someone else had waited his moment and, at the exact instant when Colonel Luttrell had fired (at a rabbit), this other person had fired at Mrs. Luttrell. Then only the one shot would have been heard. Or, even with a slight discrepancy, it would have been put down as an echo. (Now I come to think of it, there had been an echo, surely.) But no, that was absurd. There were ways of deciding exactly what weapon a bullet had been fired from. The marks on the bullet must agree with the rifling of the barrel.

But that, I remembered, was only when the police

were anxious to establish what weapon had fired the shot. There would have been no enquiry in this business. For Colonel Luttrell would have been quite as certain as everyone else that it was he who had fired the fatal shot. That fact would have been admitted, accepted without question, there would have been no question of tests. The only doubt would have been whether the shot was fired accidentally or with criminal intent - a question that could never be resolved. And therefore the case fell into line exactly with those other cases - with the case of the labourer Riggs, who didn't remember but supposed he must have done it; with Maggie Litchfield, who went out of her mind and gave herself up - for a crime she had not committed.

Yes, this case fell into line with the rest and I knew now the meaning of Poirot's manner. He was waiting for me to appreciate the fact.

TEN

I opened the subject with Poirot the following morning. His face lighted up and he wagged his head appreciatively.

"Excellent, Hastings. I wondered if you would see the similarity. I did not want to prompt you, you understand."

"Then I am right. This is another X case?"

"Undeniably."

"But why, Poirot? What is the motive?"

Poirot shook his head.

"Don't you know? Haven't you any idea?" Poirot said slowly: "I have an idea, yes."