Poirot nodded approval.

‘Anything else?’

‘Yes, sir, this chair was drawn out a little more.’ he indicated a big grandfather chair to the left of the door between it and the window. I append a plan of the room with the chair in question marked with an X.

‘Just show me,’ said Poirot.

The butler drew the chair in question out a good two feet from the wall, turning it so that the seat faced the door.

‘Voilà ce qui est curieux,’ murmured Poirot. ‘No one would want to sit in a chair in such a position, I fancy. Now who pushed it back into place again, I wonder? did you, my friend?’

‘No, sir,’ said Parker. ‘I was too upset with seeing the master and all.’

Poirot looked across at me.

‘Did you, doctor?’

I shook my head.

‘It was back in position when I arrived with the police, sir,’ put in Parker. ‘I’m sure of that.’

‘Curious,’ said Poirot again.

‘Raymond or Blunt must have pushed it back,’ I suggested. ‘Surely it isn’t important?’

‘It is completely unimportant,’ said Poirot. ‘That is why it is so interesting,’ he added softly.

‘Excuse me a minute,’ said colonel Melrose. he left the room with Parker.

‘Do you think Parker is speaking the truth?’ I asked.

‘About the chair, yes. otherwise I do not know. you will find, M. le docteur, if you have much to do with cases of this kind, that they all resemble each other in one thing.’

‘What is that?’ I asked curiously.

‘Everyone concerned in them has something to hide.’

‘Have I?’ I asked, smiling.

Poirot looked at me attentively.

‘I think you have,’ he said quietly.

‘But-’

‘Have you told me everything known to you about this young man Paton?’ He smiled as I grew red. ‘Oh! do not fear. I will not press you. I shall learn it in good time.’

‘I wish you’d tell me something of your methods,’ I said hastily, to cover my confusion. ‘The point about the fire, for instance?’

‘Oh! That was very simple. You leave Mr Ackroyd at – ten minutes to nine, was it not?’

‘Yes, exactly, I should say.’

‘The window is then closed and bolted and the door unlocked. At a quarter past ten when the body is discovered, the door is locked and the window is open. Who opened it? Clearly only Mr Ackroyd himself could have done so, and for one of two reasons. Either because the room became unbearably hot, but since the fire was nearly out and there was a sharp drop in temperature last night, that cannot be the reason, or because he admitted someone that way. And if he admitted someone that way, it must have been someone well known to him, since he had previously shown himself uneasy on the subject of that same window.’

‘It sounds very simple,’ I said.

‘Everything is simple, if you arrange the facts methodically. We are concerned now with the personality of the person who was with him at nine-thirty last night. everything goes to show that that was the individual admitted by the window, and though Mr Ackroyd was seen alive later by Miss Flora, we cannot approach a solution of the mystery until we know who that visitor was. The window may have been left open after his departure and so afforded entrance to the murderer, or the same person may have returned a second time. Ah! here is the colonel who returns.’

Colonel Melrose entered with an animated manner.

‘That telephone call has been traced at last,’ he said. ‘It did not come from here. It was put through to Dr Sheppard at 10.15 last night from a public call office at king’s Abbot station. And at 10.23 the night mail leaves for Liverpool.’

We looked at each other.

‘You’ll have inquiries made at the station, of course?’ I said.

‘Naturally, but I’m not over sanguine as to the result. you know what that station is like.’

I did. king’s Abbot is a mere village, but its station happens to be an important junction. Most of the big expresses stop there, and trains are shunted, re-sorted, and made up. It has two or three public telephone boxes. At that time of night, three local trains come in close upon each other, to catch the connection with the express for the north which comes in at 10.19 and leaves at 10.23. The whole place is in a bustle, and the chances of one particular person being noticed telephoning or getting into the express are very small indeed.

‘But why telephone at all?’ demanded Melrose. ‘That is what I find so extraordinary. There seems no rhyme or reason in the thing.’

Poirot carefully straightened a china ornament on one of the bookcases.

‘Be sure there was a reason,’ he said over his shoulder.

‘But what reason could it be?’

‘When we know that, we shall know everything. This case is very curious and very interesting.’

There was something almost indescribable in the way he said those last words. I felt that he was looking at the case from some peculiar angle of his own, and what he saw I could not tell. he went to the window and stood there, looking out.

‘You say it was nine o’clock, dr Sheppard, when you met this stranger outside the gate?’

He asked the question without turning round.

‘Yes,’ I replied. ‘I heard the church clock chime the hour.’

‘How long would it take him to reach the house – to reach this window, for instance?’

‘Five minutes at the outside. Two or three minutes only if he took the path at the right of the drive and came straight here.’

‘But to do that he would have to know the way. how can I explain myself? – it would mean that he had been here before – that he knew his surroundings.’

‘That is true,’ replied colonel Melrose.

‘We could find out, doubtless, if Mr Ackroyd had received any strangers during the past week?’

‘Young Raymond could tell us that,’ I said.

‘Or Parker,’ suggested colonel Melrose.

‘Ou tous les deux,’ suggested Poirot, smiling.

Colonel Melrose went in search of Raymond, and I rang the bell once more for Parker. Colonel Melrose returned almost immediately, accompanied by the young secretary, whom he introduced to Poirot. Geoffrey Raymond was fresh and debonair as ever. He seemed surprised and delighted to make Poirot’s acquaintance.

‘No idea you’d been living among us incognito, M. Poirot,’ he said. ‘It will be a great privilege to watch you at work – hallo, what’s this?’

Poirot had been standing just to the left of the door. Now he moved aside suddenly, and I saw that while my back was turned he must have swiftly drawn out the armchair till it stood in the position Parker had indicated.

‘Want me to sit in the chair whilst you take a blood test?’ asked Raymond good-humouredly. ‘What’s the idea?’

‘M. raymond, this chair was pulled out – so – last night when Mr Ackroyd was found killed. Someone moved it back again into place. Did you do so?’

The secretary’s reply came without a second’s hesitation. ‘No, indeed I didn’t. I don’t even remember that it was in that position, but it must have been if you say so. Anyway, somebody else must have moved it back to its proper place. Have they destroyed a clue in doing so? Too bad!’

‘It is of no consequence,’ said the detective. ‘of no consequence whatever. What I really want to ask you is this, M. raymond: did any stranger come to see Mr Ackroyd during this past week?’