‘That’s simple enough. Search everybody.’

Lord Mayfield made a movement of dissent, but Poirot spoke before he could.

‘No, no, it is not so simple as that. The person who took those plans will anticipate that a search will be made and will make quite sure that they are not found amongst his or her belongings. They will have been hidden in neutral ground.’

‘Do you suggest that we’ve got to go playing hide and seek all over the bally house?’

Poirot smiled.

‘No, no, we need not be so crude as that. We can arrive at the hiding-place (or alternatively at the identity of the guilty person) by reflection. That will simplify matters. In the morning I would like an interview with every person in the house. It would, I think, be unwise to seek those interviews now.’

Lord Mayfield nodded.

‘Cause too much comment,’ he said, ‘if we dragged everybody out of their beds at three in the morning. In any case you’ll have to proceed with a good deal of camouflage, M. Poirot. This matter has got to be kept dark.’

Poirot waved an airy hand.

‘Leave it to Hercule Poirot. The lies I invent are always most delicate and most convincing. Tomorrow, then, I conduct my investigations. But tonight, I should like to begin by interviewing you, Sir George and you, Lord Mayfield.’

He bowed to them both.

‘You mean—alone?’

‘That was my meaning.’

Lord Mayfield raised his eyes slightly, then he said:

‘Certainly. I’ll leave you alone with Sir George. When you want me, you’ll find me in my study. Come, Carlile.’

He and the secretary went out, shutting the door behind them.

Sir George sat down, reaching mechanically for a cigarette. He turned a puzzled face to Poirot.

‘You know,’ he said slowly. ‘I don’t quite get this.’

‘That is very simply explained,’ said Poirot with a smile. ‘In two words, to be accurate. Mrs Vanderlyn!’

‘Oh,’ said Carrington. ‘I think I see. Mrs Vanderlyn?’

‘Precisely. It might be, you see, that it would not be very delicate to ask Lord Mayfield the question I want to ask. Why Mrs Vanderlyn? This lady, she is known to be a suspicious character. Why, then, should she be here? I say to myself there are three explanations. One, that Lord Mayfield has a penchant for the lady (and that is why I seek to talk to you alone. I do not wish to embarrass him). Two, that Mrs Vanderlyn is perhaps the dear friend of someone else in the house?’

‘You can count me out!’ said Sir George with a grin.

‘Then, if neither of those cases is true, the question returns in redoubled force. Why Mrs Vanderlyn? And it seems to me I perceive a shadowy answer. There was a reason. Her presence at this particular juncture was definitely desired by Lord Mayfield for a special reason. Am I right?’

Sir George nodded.

‘You’re quite right,’ he said. ‘Mayfield is too old a bird to fall for her wiles. He wanted her here for quite another reason. It was like this.’