He caught up Guerchard on the stairs and said, “I will come with you, if I may, M. Guerchard. I find all these investigations extraordinarily interesting. I have been observing M. Formery’s methods—I should like to watch yours, for a change.”

“By all means,” said Guerchard. “And there are several things I want to hear about from your Grace. Of course it might be an advantage to discuss them together with M. Formery, but—” and he hesitated.

“It would be a pity to disturb M. Formery in the middle of the process of reconstruction,” said the Duke; and a faint, ironical smile played round the corners of his sensitive lips.

Guerchard looked at him quickly: “Perhaps it would,” he said.

They went through the house, out of the back door, and into the garden. Guerchard moved about twenty yards from the house, then he stopped and questioned the Duke at great length. He questioned him first about the Charolais, their appearance, their actions, especially about Bernard’s attempt to steal the pendant, and the theft of the motor-cars.

“I have been wondering whether M. Charolais might not have been Arsène Lupin himself,” said the Duke.

“It’s quite possible,” said Guerchard. “There seem to be no limits whatever to Lupin’s powers of disguising himself. My colleague, Ganimard, has come across him at least three times that he knows of, as a different person. And no single time could he be sure that it was the same man. Of course, he had a feeling that he was in contact with some one he had met before, but that was all. He had no certainty. He may have met him half a dozen times besides without knowing him. And the photographs of him—they’re all different. Ganimard declares that Lupin is so extraordinarily successful in his disguises because he is a great actor. He actually becomes for the time being the person he pretends to be. He thinks and feels absolutely like that person. Do you follow me?”

“Oh, yes; but he must be rather fluid, this Lupin,” said the Duke; and then he added thoughtfully, “It must be awfully risky to come so often into actual contact with men like Ganimard and you.”

“Lupin has never let any consideration of danger prevent him doing anything that caught his fancy. He has odd fancies, too. He’s a humourist of the most varied kind—grim, ironic, farcical, as the mood takes him. He must be awfully trying to live with,” said Guerchard.

“Do you think humourists are trying to live with?” said the Duke, in a meditative tone. “I think they brighten life a good deal; but of course there are people who do not like them—the middle-classes.”