“But, mon ami, what you say, it is ridiculous,” Poirot spluttered. “It is not logical. The ‘now’ was there, in the sentence. We cannot pretend to be without it when we are with it. We cannot ignore a ‘now’ that is right in front of our ears!”

“I’m afraid I disagree with you,” I said with some trepidation. “If I had to guess, I should say that the intended meaning was something along these lines: before she let herself go, this chap didn’t especially mind or notice the age difference between them. Maybe it wasn’t quite so visible. However, now that she is no longer in tip-top shape, the chap has moved on to a younger, more attractive companion, the one he now confides in—”

Poirot had begun to speak over me, red faced and impatient. “There is no point in your guessing, Catchpool, when I know! Listen to Poirot! Listen one more time to exactly what was said, and in what order: ‘He’d hardly be interested in her now—she’s let herself go, and she’s old enough to be his mother!’ Reason one that he would no longer be interested in her, followed by reason two! The construction of the sentence makes it clear that both of these unfortunate circumstances that are the case now were once not the case.”

“There is no need to shout at me, Poirot. I have grasped your point, and I still disagree. Not everybody is as precise in their speech as you are. My interpretation has to be the correct one, and yours incorrect, because, as you have pointed out, it makes no sense otherwise. You said it yourself: if she is old enough to be his mother now, then she must always have been old enough to be his mother.”

“Catchpool, Catchpool. How I begin to despair of you! Think of what came later in the same conversation. Rafal Bobak heard Samuel Kidd, posing as Richard Negus, say, ‘I dispute the old-enough-to-be-his-mother claim. I dispute it utterly.’ To which Nancy, posing as Harriet, replied, ‘Well, neither of us can prove we’re right, so let’s agree to disagree!’ But why could neither prove they were right? Surely it is a matter of simple biological fact whether or not a woman is old enough to be a man’s mother? If she is four years older than him, then she is not old enough. No one would dispute this! If she is twenty years older, then she is old enough to be his mother—that is equally certain.”

“What if she were thirteen years older?” said Jennie Hobbs, who had closed her eyes. “Or twelve? One does hear of rare cases . . . That does not apply here, of course.”

So Jennie knew where Poirot was going with all this. I was the only ignorant one in the room.