‘I think I must try to make my explanation a little more subtle,’ said Sir Henry, ‘though I admit it’s only a guess. I suggest that Miss Barton was always mentally unhinged. There are more cases like that than you would imagine. Her mania grew stronger and she began to believe it her duty to rid the world of certain persons—possibly what is termed unfortunate females. Nothing much is known about Miss Durrant’s past. So very possibly she had a past—an “unfortunate” one. Miss Barton learns of this and decides on extermination. Later, the righteousness of her act begins to trouble her and she is overcome by remorse. Her end shows her to be completely unhinged. Now, do say you agree with me, Miss Marple.’

‘I’m afraid I don’t, Sir Henry,’ said Miss Marple, smiling apologetically. ‘I think her end shows her to have been a very clever and resourceful woman.’

Jane Helier interrupted with a little scream.

‘Oh! I’ve been so stupid. May I guess again? Of course it must have been that. Blackmail! The companion woman was blackmailing her. Only I don’t see why Miss Marple says it was clever of her to kill herself. I can’t see that at all.’

‘Ah!’ said Sir Henry. ‘You see, Miss Marple knew a case just like it in St Mary Mead.’

‘You always laugh at me, Sir Henry,’ said Miss Marple reproachfully. ‘I must confess it does remind me, just a little, of old Mrs Trout. She drew the old age pension, you know, for three old women who were dead, in different parishes.’

‘It sounds a most complicated and resourceful crime,’ said Sir Henry. ‘But it doesn’t seem to me to throw any light upon our present problem.’

‘Of course not,’ said Miss Marple. ‘It wouldn’t—to you. But some of the families were very poor, and the old age pension was a great boon to the children. I know it’s difficult for anyone outside to understand. But what I really meant was that the whole thing hinged upon one old woman being so like any other old woman.’

‘Eh?’ said Sir Henry, mystified.

‘I always explain things so badly. What I mean is that when Dr Lloyd described the two ladies first, he didn’t know which was which, and I don’t suppose anyone else in the hotel did. They would have, of course, after a day or so, but the very next day one of the two was drowned, and if the one who was left said she was Miss Barton, I don’t suppose it would ever occur to anyone that she mightn’t be.’

‘You think—Oh! I see,’ said Sir Henry slowly.

‘It’s the only natural way of thinking of it. Dear Mrs Bantry began that way just now. Why should the rich employer kill the humble companion? It’s so much more likely to be the other way about. I mean—that’s the way things happen.’

‘Is it?’ said Sir Henry. ‘You shock me.’

‘But of course,’ went on Miss Marple, ‘she would have to wear Miss Barton’s clothes, and they would probably be a little tight on her, so that her general appearance would look as though she had got a little fatter. That’s why I asked that question. A gentleman would be sure to think it was the lady who had got fatter, and not the clothes that had got smaller—though that isn’t quite the right way of putting it.’