The whole thing was simplicity itself, and by the aid of Miss Gannett, who co-operated loyally, at once giving Clara leave of absence, the matter was rushed through at express speed.

It was when we were sitting down to lunch that Caroline remarked, with would-be unconcern: 'About those boots of Ralph Paton's.' 'Well,' I said, 'what about them?' 'M. Poirot thought they were probably brown. He was wrong. They're black.' And Caroline nodded her head several times. She evidently felt that she had scored a point over Poirot.

I did not answer. I was puzzling over what the colour of a pair of Ralph Paton's boots had to do with the case.

I was to have a further proof that day of the success of Poirot's tactics. That challenge of his had been a subtle touch born of his knowledge of human nature. A mixture of fear and guilt had wrung the truth from Mrs Ackroyd. She was the first to react.

That afternoon when I returned from seeing my patients, Caroline told me that Geoffrey Raymond had just left.

'Did he want to see me?' I asked, as I hung up my coat in the hall.

Caroline was hovering by my elbow.

'It was M. Poirot he wanted to see,' she said. 'He'd just come from the Larches. Mr. Poirot was out. Mr Raymond thought that he might be here, or that you might know where he was.' 'I haven't the least idea.' 'I tried to make him wait,' said Caroline, 'but he said he would call back at The Larches in half an hour, and went away down the village. A great pity, because M. Poirot came in practically the minute after he left.' 'Came in here?' 'No, to his own house.' 'How do you know?' 'The side window,' said Caroline briefly.

It seemed to me that we had now exhausted the topic.

Caroline thought otherwise.

'Aren't you going across?' 'Across where?' 'To The Larches, of course.' 'My dear Caroline,' I said, 'what for?' 'Mr Raymond wanted to see him very particularly' said Caroline. 'You might hear what it's all about.' I raised my eyebrows.

'Curiosity is not my besetting sin,' I remarked coldly. 'I can exist comfortably without knowing exactly what my neighbours are doing and thinking.' 'Stuff and nonsense, James,' said my sister. 'You want to know just as much as I do. You're not so honest, that's all.

You always have to pretend.' 'Really, Caroline,' I said, and retired into my surgery.

Ten minutes later Caroline tapped at the door and entered.

In her hand she held what seemed to be a pot of jam.

'I wonder, James,' she said, 'if you would mind taking this pot of medlar jelly across to M. Poirot? I promised it to him.

He has never tasted any home-made medlar jelly.' 'Why can't Annie go?' I asked coldly.

'She's doing some mending. I can't spare her.' Caroline and I looked at each other.

'Very well,' I said, rising. 'But if I take the beastly thing, I shall just leave it at the door. You understand that?' My sister raised her eyebrows.

'Naturally,' she said. 'Who suggested you should do anything else?' The honours were with Caroline.

'If you do happen to see M. Poirot,' she said, as I opened the front door, 'you might tell him about the boots.' It was a most subtle parting shot. I wanted dreadfully to understand the enigma of the boots. When the old lady with the Breton cap opened the door to me, I found myself asking if M. Poirot was in, quite automatically.

Poirot sprang up to meet me, with every appearance of pleasure.

'Sit down, my good friend,' he said. 'The big chair? This small one? The room is not too hot, no?' I thought it was stifling, but refrained from saying so. The windows were closed, and a large fire burned in the grate.

'The English people, they have a mania for the fresh air,' declared Poirot. 'The big air, it is all very well outside, where it belongs. Why admit it to the house? But let us not discuss such banalities. You have something for me, yes?' 'Two things,' I said. 'First - this - from my sister.' I handed over the pot of medlar jelly.

'How kind of Mademoiselle Caroline. She has remembered her promise. And the second thing?' 'Information - of a kind.' And I told him of my interview with Mrs Ackroyd. He listened with interest, but not much excitement.

'It clears the ground,' he said thoughtfully. 'And it has a certain value as confirming the evidence of the housekeeper.

She said, you remember, that she found the silver table lid open and closed it down in passing.' 'What about her statement that she went into the drawing-room to see if the flowers were fresh?' 'Ah! we never took that very seriously, did we, my friend? It was patently an excuse, trumped up in a hurry, by a woman who felt it urgent to explain her presence - which, by the way, you would probably never have thought of questioning. I considered it possible that her agitation might arise from the fact that she had been tampering with the silver table, but I think now that we must look for another cause.' 'Yes,' I said. 'Whom did she go out to meet? And why?' 'You think she went to meet someone?' 'I do.' Poirot nodded.

'So do I,' he said thoughtfully.

There was a pause.

'By the way,' I said, 'I've got a message for you from my sister. Ralph Paton's boots were black, not brown.' I was watching him closely as I gave the message, and I fancied that I saw a momentary flicker of discomposure. If so, it passed almost immediately.

'She is absolutely positive they are not brown?' 'Absolutely.' 'Ah!' said Poirot regretfully. 'That is a pity.' And he seemed quite crestfallen.

He entered into no explanations, but at once started a new subject of conversation.

'The housekeeper, Miss Russell, who came to consult you on that Friday morning - is it indiscreet to ask what passed at the interview - apart from the medical details, I mean?' 'Not at all,' I said. 'When the professional part of the conversation was over, we talked for a few minutes about poisons, and the ease or difficulty of detecting them, and about drug-taking and drug-takers.' 'With special reference to cocaine?' asked Poirot.

'How did you know?' I asked, somewhat surprised.

For answer, the little man rose and crossed the room to where newspapers were filed. He brought me a copy of the Daily Budget, dated Friday, 16th September, and showed me an article dealing with the smuggling of cocaine. It was a somewhat lurid article, written with an eye to picturesque effect.

'That is what put cocaine into her head, my friend,' he said.

I would have catechized him further, for I did not quite understand his meaning, but at that moment the door opened and Geoffrey Raymond was announced.

He came in fresh and debonair as ever, and greeted us both.

'How are you, doctor? M. Poirot, this is the second time I've been here this morning. I was anxious to catch you.' 'Perhaps I'd better be off,' I suggested rather awkwardly.

'Not on my account, doctor. No, it's just this,' he went on, seating himself at a wave of invitation from Poirot, 'I've got a confession to make.' 'En verite?' said Poirot, with an air of polite interest.

'Oh, it's of no consequence, really. But, as a matter of fact, my conscience has been pricking me ever since yesterday afternoon. You accused us all of keeping back something, M. Poirot. I plead guilty. I've had something up my sleeve.' 'And what is that, M. Raymond?' 'As I say, it's nothing of consequence- just this. I was in debt - badly, and that legacy came in the nick of time. Five hundred pounds puts me on my feet again with a little to spare.' He smiled at us both with that engaging frankness that made him such a likeable youngster.

'You know how it is. Suspicious-looking policemen - don't like to admit you were hard up for money - think it will look bad to them. But I was a fool, really, because Blunt and I were in the billiard room from a quarter to ten onwards, so I've got a watertight alibi and nothing to fear. Still, when you thundered out that stuff about concealing things, I felt a nasty prick of conscience, and I thought I'd like to get it off my mind.' He got up again and stood smiling at us.