“Of course, of course,” said M. Formery, taking him up quickly. “The burglars came here with their boots covered with plaster. They’ve swept away all the other marks of their feet from the carpet; but whoever did the sweeping was too slack to lift up that book and sweep under it. This footprint, however, is not of great importance, though it is corroborative of all the other evidence we have that they came and went by the garden. There’s the ladder, and that table half out of the window. Still, this footprint may turn out useful, after all. You had better take the measurements of it, inspector. Here’s a foot-rule for you. I make a point of carrying this foot-rule about with me, your Grace. You would be surprised to learn how often it has come in useful.” He took a little ivory foot-rule from his waist-coat pocket, and gave it to the inspector, who fell on his knees and measured the footprint with the greatest care. “I must take a careful look at that house they’re building. I shall find a good many traces there, to a dead certainty,” said M. Formery. The inspector entered the measurements of the footprint in his note-book. There came the sound of a knocking at the front door. “I shall find footprints of exactly the same dimensions as this one at the foot of some heap of plaster beside that house,” said M. Formery; with an air of profound conviction, pointing through the window to the house building beyond the garden. A policeman opened the door of the drawing-room and saluted. “If you please, sir, the servants have arrived from Charmerace,” he said. “Let them wait in the kitchen and the servants’ offices,” said M. Formery. He stood silent, buried in profound meditation, for a couple of minutes. Then he turned to the Duke and said, “What was that you said about a theft of motor-cars at Charmerace?” “When he received the letter from Arsène Lupin, M. Gournay-Martin decided to start for Paris at once,” said the Duke. “But when we sent for the cars we found that they had just been stolen. M. Gournay-Martin’s chauffeur and another servant were in the garage gagged and bound. Only an old car, a hundred horse-power Mercrac, was left. I drove it to Paris, leaving M. Gournay-Martin and his family to come on by train.” “Very important—very important indeed,” said M. Formery. He thought for a moment, and then added. “Were the motor-cars the only things stolen? Were there no other thefts?”