Poirot made a gesture for me to stay after everyone had left. I was puzzled. There had been a real threat in Poirot's words - hut I still believed he had the wrong idea.

He moved over to the fireplace. 'Well, my friend,' he said quietly, 'and what do you think of it all?'

'I don't know what to think. Why not go straight to Inspector Raglan with the truth instead of giving the guilty person this warning?'

Poirot sat down. 'Use your little grey cells,' he said. 'There is always a reason behind my actions.'

I said slowly, 'It seems to me that the first reason was to try and force a confession from the murderer?'

'A clever idea, but not the truth.'

'My second thought is that, perhaps, by making him believe you knew, you might force him out into the open. He might try to silence you as he formerly silenced Mr Ackroyd.'

'And use myself to trap him? Mon ami, I am not sufficiently heroic for that.'

'Then surely you are running the risk of letting the murderer escape by warning him?'

Poirot shook his head. 'He cannot escape. There is only one way out - and that way does not lead to freedom.'

'You really believe that one of those people here tonight committed the murder?' I asked.

'Yes, my friend. I will explain exactly how I reached my conclusion. Now, there were two facts and a little discrepancy in time which attracted my attention. The first was the telephone call. If Ralph Paton was indeed the murderer, the telephone call became meaningless and silly. Therefore, I said to myself, Ralph Paton is not the murderer. I concluded that the telephone call must have been made by an accomplice of the murderer. I was not quite pleased with that deduction, but I let it stand for the minute.

'I next examined the motive for the call. That was difficult. I could only get at it by judging its result. Which was - that the murder was discovered that night instead of the following morning. But matters were still not clear. What was the advantage of having the crime discovered that night rather than the following morning? The only idea I had was that the murderer, knowing the crime was to be discovered at a certain time, could make sure of being present when the door was broken in - or immediately afterwards.