“All these houses must be connected by secret passages, but I can’t find them.”

For the first time in his life, Wilson doubted the omnipotence of his famous associate. Why did he now talk so much and accomplish so little?

“Why?” exclaimed Sholmes, in answer to Wilson’s secret thought, “because, with this fellow Lupin, a person has to work in the dark, and, instead of deducting the truth from established facts, a man must extract it from his own brain, and afterward learn if it is supported by the facts in the case.”

“But what about the secret passages?”

“They must exist. But even though I should discover them, and thus learn how Arsène Lupin made his entrance to the lawyer’s house and how the blonde Lady escaped from the house of Baron d’Hautrec after the murder, what good would it do? How would it help me? Would it furnish me with a weapon of attack?”

“Let us attack him just the same,” exclaimed Wilson, who had scarcely uttered these words when he jumped back with a cry of alarm. Something had fallen at their feet; it was a bag filled with sand which might have caused them serious injury if it had struck them.

Sholmes looked up. Some men were working on a scaffolding attached to the balcony at the fifth floor of the house. He said:

“We were lucky; one step more, and that heavy bag would have fallen on our heads. I wonder if—”

Moved by a sudden impulse, he rushed into the house, up the five flights of stairs, rang the bell, pushed his way into the apartment to the great surprise and alarm of the servant who came to the door, and made his way to the balcony in front of the house. But there was no one there.

“Where are the workmen who were here a moment ago?” he asked the servant.