That was true enough. I never saw him do it. And I’m sure Mr Mercado hadn’t suspected. He must have been quick as lightning.

‘But, M. Poirot, why?’ I asked.

He answered me by another question.

‘Did you notice anything, sister?’ he asked.

I nodded my head slowly.

‘Hypodermic marks,’ I said.

‘So now we know something about Mr Mercado,’ said Poirot. ‘I suspected – but I did not know. It is always necessary to know.’

‘And you don’t care how you set about it!’ I thought, but didn’t say.

Poirot suddenly clapped his hand to his pocket.

‘Alas, I have dropped my handkerchief down there. I concealed the pin in it.’

‘I’ll get it for you,’ I said and hurried back.

I’d got the feeling, you see, by this time, that M. Poirot and I were the doctor and nurse in charge of a case. At least, it was more like an operation and he was the surgeon. Perhaps I oughtn’t to say so, but in a queer way I was beginning to enjoy myself.

I remember just after I’d finished my training, I went to a case in a private house and the need for an immediate operation arose, and the patient’s husband was cranky about nursing homes. He just wouldn’t hear of his wife being taken to one. Said it had to be done in the house.

Well, of course it was just splendid for me! Nobody else to have a look in! I was in charge of everything. Of course, I was terribly nervous – I thought of everything conceivable that doctor could want, but even then I was afraid I might have forgotten something. You never know with doctors. They ask for absolutely anything sometimes! But everything went splendidly! I had each thing ready as he asked for it, and he actually told me I’d done first-rate after it was over – and that’s a thing most doctors wouldn’t bother to do! The G.P. was very nice too. And I ran the whole thing myself!

The patient recovered, too, so everybody was happy.

Well, I felt rather the same now. In a way M. Poirot reminded me of that surgeon. He was a little man, too. Ugly little man with a face like a monkey, but a wonderful surgeon. He knew instinctively just where to go. I’ve seen a lot of surgeons and I know what a lot of difference there is.

Gradually I’d been growing a kind of confidence M. Poirot. I felt that he, too, knew exactly what he was doing. And I was getting to feel that it was my job to help him – as you might say – to have the forceps and the swabs and all handy just when he wanted them. That’s why it seemed just as natural for me to run off and look for his handkerchief as it would have been to pick up a towel that a doctor had thrown on the floor.

When I’d found it and got back I couldn’t see him at first. But at last I caught sight of him. He was sitting a little way from the mound talking to Mr Carey. Mr Carey’s boy was standing near with that great big rod thing with metres marked on it, but just at that moment he said something to the boy and the boy took it away. It seemed he had finished with it for the time being.

I’d like to get this next bit quite clear. You see, I wasn’t quite sure what M. Poirot did or didn’t want me to do. He might, I mean, have sent me back for that handkerchiefon purpose. To get me out of the way.

It was just like an operation over again. You’ve got to be careful to hand the doctor just what he wants and not what he doesn’t want. I mean, suppose you gave him the artery forceps at the wrong moment, and were late with them at the right moment! Thank goodness I know my work in the theatre well enough. I’m not likely to make mistakes there. But in this business I was really the rawest of raw little probationers. And so I had to be particularly careful not to make any silly mistakes.

Of course, I didn’t for one moment imagine that M. Poirot didn’t want me to hear what he and Mr Carey were saying. But he might have thought he’d get Mr Carey to talk better if I wasn’t there.

Now I don’t want anybody to get it in to their heads that I’m the kind of woman who goes about eavesdropping on private conversations. I wouldn’t do such a thing. Not for a moment. Not however much I wanted to.

And what I mean is if it had been a private conversation I wouldn’t for a moment have done what, as a matter of fact, I actually did do.

As I looked at it I was in a privileged position. After all, you hear many a thing when a patient’s coming round after an anaesthetic. The patient wouldn’t want you to hear it – and usually has no idea you have heard it – but the fact remains you do hear it. I just took it that Mr Carey was the patient. He’d be none the worse for what he didn’t know about. And if you think that I was just curious, well, I’ll admit that I was curious. I didn’t want to miss anything I could help.

All this is just leading up to the fact that I turned aside and went by a round about way up behind the big dump until I was a foot from where they were, but concealed from them by the corner of the dump. And if anyone says it was dishonourable I just beg to disagree. Nothing ought to be hidden from the nurse in charge of the case, though, of course, it’s for the doctor to say what shall be done.

I don’t know, of course, what M. Poirot’s line of approach had been, but by the time I’d got there he was aiming straight for the bull’s eye, so to speak.

‘Nobody appreciates Dr Leidner’s devotion to his wife more than I do,’ he was saying. ‘But it is often the case that one learns more about a person from their enemies than from their friends.’

‘You suggest that their faults are more important than their virtues?’ said Mr Carey. His tone was dry and ironic.

‘Undoubtedly – when it comes to murder. It seems odd that as far as I know nobody has yet been murdered for having too perfect a character! And yet perfection is undoubtedly an irritating thing.’

‘I’m afraid I’m hardly the right person to help you,’ said Mr Carey. ‘To be perfectly honest, Mrs Leidner and I didn’t hit it off particularly well. I don’t mean that we were in any sense of the word enemies, but we were not exactly friends. Mrs Leidner was, perhaps, a shade jealous of my old friendship with her husband. I, for my part, although I admired her very much and thought she was an extremely attractive woman, was just a shade resentful of her influence over Leidner. As a result we were quite polite to each other, but not intimate.’

‘Admirably explained,’ said Poirot.

I could just see their heads, and I saw Mr Carey’s turn sharply as though something in M. Poirot’s detached tone struck him disagreeably.

M. Poirot went on: ‘Was not Dr Leidner distressed that you and his wife did not get on together better?’

Carey hesitated a minute before saying: ‘Really – I’m not sure. He never said anything. I always hoped he didn’t notice it. He was very wrapped up in his work, you know.’

‘So the truth, according to you, is that you did not really like Mrs Leidner?’

Carey shrugged his shoulders.

‘I should probably have liked her very much if she hadn’t been Leidner’s wife.’

He laughed as though amused by his own statement.

Poirot was arranging a little heap of broken potsherds. He said in a dreamy, far-away voice: ‘I talked to Miss Johnson this morning. She admitted that she was prejudiced against Mrs Leidner and did not like her very much, although she hastened to add that Mrs Leidner had always been charming to her.’

‘All quite true, I should say,’ said Carey.

‘So I believed. Then I had a conversation with Mrs Mercado. She told me at great length how devoted she had been to Mrs Leidner and how much she had admired her.’

Carey made no answer to this, and after waiting a minute or two Poirot went on: ‘That – I did not believe! Then I come to you and that which you tell me – well, again – I do not believe…’

Carey stiffened. I could hear the anger – repressed anger – in his voice.

‘I really cannot help your beliefs – or your disbeliefs, M. Poirot. You’ve heard the truth and you can take it or leave it as far as I am concerned.’