Stammering a little, as he always did when he was serious about a thing, he embarked on an involved story centering on a point of ethics.

"You know, Hastings, it should be awfully simple to say when a thing's right or wrong - but really, when it comes to it, it isn't quite such plain sailing. I mean one may come across something - the kind of thing, you see, that isn't meant for you - it's all a kind of accident, and it's the sort of thing you couldn't take advantage of, and yet it might be most frightfully important. Do you see what I mean?"

"Not very well, I'm afraid," I confessed.

Norton's brow furrowed again. He ran his hands up through his hair again so that it stood upright in its usual comical manner.

"It's so hard to explain. What I mean is, suppose you just happened to see something in a private letter - one opened by mistake, that sort of thing - a letter meant for someone else and you began reading it because you thought it was written to you and so you actually read something you weren't meant to before you realized. That could happen, you know."

"Oh yes, of course it could."

"Well, I mean, what would one do?"

"Well - " I gave my mind to the problem. "I suppose you'd go to the person and say: 'I'm awfully sorry, but I opened this by mistake.' " Norton sighed. He said it wasn't quite so simple as that.

"You see - you might have read something rather embarrassing, Hastings."

"That would embarrass the other person, you mean? I suppose you'd have to pretend you hadn't actually read anything - that you'd discovered your mistake in time."

"Yes." Norton said it after a moment's pause, and he did not seem to feel that he had yet arrived at a satisfactory solution.

He said rather wistfully:

"I wish I did know what I ought to do."

I said that I couldn't see that there was anything else he could do. Norton said, the perplexed frown still on his forehead:

"You see, Hastings, there's rather more to it than that. Supposing that what you read was - well, rather important to someone else again, I mean." I lost patience.

"Really, Norton, I don't see what you do mean. You can't go about reading other people's private letters, can you - "

"No, no, of course not. I didn't mean that. And anyway, it wasn't a letter at all. I only said that to try and explain the sort of thing. Naturally anything you saw or heard or read - by accident - you'd keep to yourself, unless - "

"Unless what?"

Norton said slowly:

"Unless it was something you ought to speak about." I looked at him with suddenly awakened interest. He went on:

"Look here, think of it this way - supposing you saw something through a - a keyhole - "

Keyholes made me think of Poirot! Norton was stumbling on: