“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.”

He retailed the conversation that had taken place at the dinner table. Poirot listened attentively.

“Ah,” he said. “I comprehend now. Nevertheless, it seems that the lady has turned the tables on you both rather neatly!”

Sir George swore freely.

Poirot watched him with some slight amusement, then he said:

“You do not doubt that this theft is her doing—I mean, that she is responsible for it, whether or no she played an active part?”

Sir George stared.

“Of course not! There isn’t any doubt of that. Why, who else would have any interest in stealing those plans?”

“Ah!” said Hercule Poirot. He leaned back and looked at the ceiling. “And yet, Sir George, we agreed, not a quarter of an hour ago, that these papers represented very definitely money. Not perhaps, in quite so obvious a form as banknotes, or gold, or jewellery, but nevertheless they were potential money. If there were anyone here who was hard up—”

The other interrupted him with a snort.