The little man shrugged his shoulders.

‘Why not? One has only to reason—to reflect.’

He paused a moment and then said:

‘I would like now to speak to Mr Carlile.’

‘Certainly.’ Lord Mayfield rose. ‘I asked him to wait up. He will be somewhere at hand.’

He went out of the room.

Poirot looked at Sir George.

‘Eh bien,’ he said. ‘What about this man on the terrace?’

‘My dear M. Poirot. Don’t ask me! I didn’t see him, and I can’t describe him.’

Poirot leaned forward.

‘So you have already said. But it is a little different from that is it not?’

‘What d’you mean?’ asked Sir George abruptly.

‘How shall I say it? Your disbelief, it is more profound.’

Sir George started to speak, then stopped.

‘But yes,’ said Poirot encouragingly. ‘Tell me. You are both at the end of the terrace. Lord Mayfield sees a shadow slip from the window and across the grass. Why do you not see that shadow?’

Carrington stared at him.

‘You’ve hit it, M. Poirot. I’ve been worrying about that ever since. You see, I’d swear that no one did leave this window. I thought Mayfield had imagined it—branch of a tree waving—something of that kind. And then when we came in here and found there had been a robbery, it seemed as though Mayfield must have been right and I’d been wrong. And yet—’

Poirot smiled.

‘And yet you still in your heart of hearts believe in the evidence (the negative evidence) of your own eyes?’

‘You’re right, M. Poirot, I do.’

Poirot gave a sudden smile.

‘How wise you are.’

Sir George said sharply:

‘There were no footprints on the grass edge?’

Poirot nodded.

‘Exactly. Lord Mayfield, he fancies he sees a shadow. Then there comes the robbery and he is sure—but sure! It is no longer a fancy—he actually saw the man. But that is not so. Me, I do not concern myself much with footprints and such things but for what it is worth we have that negative evidence. There were no footprints on the grass. It had rained heavily this evening. If a man had crossed the terrace to the grass this evening his footprints would have shown.’

Sir George said, staring: ‘But then—but then—’

‘It brings us back to the house. To the people in the house.’

He broke off as the door opened and Lord Mayfield entered with Mr Carlile.

Though still looking very pale and worried, the secretary had regained a certain composure of manner. Adjusting his pincenez he sat down and looked at Poirot inquiringly.

‘How long had you been in this room when you heard the scream, monsieur?’

Carlile considered.

‘Between five and ten minutes, I should say.’

‘And before that there had been no disturbance of any kind?’

‘No.’

‘I understand that the house-party had been in one room for the greater part of the evening.’

‘Yes, the drawing-room.’

Poirot consulted his notebook.

‘Sir George Carrington and his wife. Mrs Macatta. Mrs Vanderlyn. Mr Reggie Carrington. Lord Mayfield and yourself. Is that right?’