That evening, at Poirot's request, I went over to his house after dinner. He had placed a bottle of whisky on a small table, with water and a glass. He himself was making hot chocolate. He inquired politely about my sister, who he said was a most interesting woman.

'You will have got all the local gossip from her,' I said. 'True, and untrue.'

'And a great deal of valuable information,' he added quietly. 'Women, they are marvelous! They observe a thousand little details, without knowing that they are doing so. Their subconscious mind adds these little things together - and they call the result intuition.'

'I wish you'd tell me', I said, 'what you really think of it all.'

'You have seen what I have seen. Should our ideas not be the same?'

'I'm afraid you're laughing at me. I've no experience of matters of this kind.'

Poirot smiled at me. 'So I give you, then, a little lecture. The first thing is to get a clear history of what happened that evening - always remembering that the person who speaks may be lying. Now first - Dr Sheppard leaves the house at ten minutes to nine. How do I know that?'

'Because I told you so.'

'You might not be speaking the truth. But Parker also says that you left the house at ten minutes to nine. So we accept that and pass on. At nine o'clock you leave the Park gates. How do I know that that is so?'

'I told you so,' I began again, but Poirot interrupted me with a gesture of impatience.

'Ah! You are a little stupid tonight, my friend. You know that it is so - but how am I to know? You do not use your little grey cells. Now, what did you think of the parlourmaid's story? Does it take half an hour to dismiss a servant? Was the story of those important papers true? Tell me now your own ideas.'

I took a piece of paper from my pocket. 'I wrote down a few suggestions,' I said.

'But excellent - you have method. Let us hear them.'

'To begin with, one must look at the thing logically...'

'Just what my poor friend Hastings used to say,' interrupted Poirot, 'but alas, he never did so!'

Point No. I

'Mr Ackroyd was heard talking to someone at half-past nine.'

Point No. 2

'At some time during the evening Ralph Paton must have come in through the window - the prints of his shoes tell us that.'

Point No. 3

'Mr Ackroyd would only have let in someone he knew.'

Point No. 4

'The person with Mr Ackroyd at nine-thirty was asking for money. We know Ralph Paton needed money.'