In carrying out Victoire, the inspector had left the door of the drawing-room open. After he had watched M. Formery reflect for two minutes, Guerchard faded—to use an expressive Americanism—through it. The Duke felt in the breast-pocket of his coat, murmured softly, "My cigarettes," and followed him.  
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 Arsene 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."
 
"Yes, yes, they're all very well in their place; but to live with they must be trying," said Guerchard quickly.
 
He went on to question the Duke closely and at length about the household of M. Gournay-Martin, saying that Arsene Lupin worked with the largest gang a burglar had ever captained, and it was any odds that he had introduced one, if not more, of that gang into it. Moreover, in the case of a big affair like this, Lupin himself often played two or three parts under as many disguises.
 
"If he was Charolais, I don't see how he could be one of M. Gournay-Martin's household, too," said the Duke in some perplexity.
 
"I don't say that he WAS Charolais," said Guerchard. "It is quite a moot point. On the whole, I'm inclined to think that he was not. The theft of the motor-cars was a job for a subordinate. He would hardly bother himself with it."
 
The Duke told him all that he could remember about the millionaire's servants—and, under the clever questioning of the detective, he was surprised to find how much he did remember—all kinds of odd details about them which he had scarcely been aware of observing.
 
The two of them, as they talked, afforded an interesting contrast: the Duke, with his air of distinction and race, his ironic expression, his mobile features, his clear enunciation and well-modulated voice, his easy carriage of an accomplished fencer—a fencer with muscles of steel—seemed to be a man of another kind from the slow-moving detective, with his husky voice, his common, slurring enunciation, his clumsily moulded features, so ill adapted to the expression of emotion and intelligence. It was a contrast almost between the hawk and the mole, the warrior and the workman. Only in their eyes were they alike; both of them had the keen, alert eyes of observers. Perhaps the most curious thing of all was that, in spite of the fact that he had for so much of his life been an idler, trifling away his time in the pursuit of pleasure, except when he had made his expedition to the South Pole, the Duke gave one the impression of being a cleverer man, of a far finer brain, than the detective who had spent so much of his life sharpening his wits on the more intricate problems of crime.
 
When Guerchard came to the end of his questions, the Duke said: "You have given me a very strong feeling that it is going to be a deuce of a job to catch Lupin. I don't wonder that, so far, you have none of you laid hands on him."
 
"But we have!" cried Guerchard quickly. "Twice Ganimard has caught him. Once he had him in prison, and actually brought him to trial. Lupin became another man, and was let go from the very dock."
 
"Really? It sounds absolutely amazing," said the Duke.
 
"And then, in the affair of the Blue Diamond, Ganimard caught him again. He has his weakness, Lupin—it's women. It's a very common weakness in these masters of crime. Ganimard and Holmlock Shears, in that affair, got the better of him by using his love for a woman—'the fair-haired lady,' she was called—to nab him."
 
"A shabby trick," said the Duke.
 
"Shabby?" said Guerchard in a tone of utter wonder. "How can anything be shabby in the case of a rogue like this?"
 
"Perhaps not—perhaps not—still—" said the Duke, and stopped.
 
The expression of wonder faded from Guerchard's face, and he went on, "Well, Holmlock Shears recovered the Blue Diamond, and Ganimard nabbed Lupin. He held him for ten minutes, then Lupin escaped."
 
"What became of the fair-haired lady?" said the Duke.
 
"I don't know. I have heard that she is dead," said Guerchard. "Now I come to think of it, I heard quite definitely that she died."
 
"It must be awful for a woman to love a man like Lupin—the constant, wearing anxiety," said the Duke thoughtfully.
 
"I dare say. Yet he can have his pick of sweethearts. I've been offered thousands of francs by women—women of your Grace's world and wealthy Viennese—to make them acquainted with Lupin," said Guerchard.
 
"You don............