A clock struck half-past six. At that moment the door of one of the houses overlooking the square opened. A man came out, closed the door behind him, crossed the Rue de Chaillot and walked round the open space in front of the museum. It was an officer in khaki. Under his red forage-cap, with its three lines of gold braid, his head was wrapped in a wide linen bandage, which hid his forehead and neck. He was tall and very slenderly built. His right leg ended in a wooden stump with a rubber foot to it. He leant on a stick. Leaving the square, he stepped into the roadway of the Rue Pierre-Charron. Here he turned and gave a leisurely look to his surroundings on every side. This minute inspection brought him to one of the trees facing the museum. With the tip of his cane he gently tapped a protruding stomach. The stomach pulled itself in. The officer moved off again. This time he went definitely down the Rue Pierre-Charron towards the center of Paris. He thus came to the Avenue des Champs-Élysées, which he went up, taking the left pavement. Two hundred yards further on was a large house, which had been transformed, as a flag proclaimed, into a hospital. The officer took up his position at some distance, so as not to be seen by those leaving, and waited. It struck a quarter to seven and seven o'clock. A few more minutes passed. Five persons came out of the house, followed by two more. At last a lady appeared in the hall, a nurse wearing a wide blue cloak marked with the Red Cross. "Here she comes," said the officer. She took the road by which he had arrived and turned down the Rue Pierre-Charron, keeping to the right-hand pavement and thus making for the space where the street meets the Rue de Chaillot. Her walk was light, her step easy and well-balanced. The wind, buffeting against her as she moved quickly on her way, swelled out the long blue veil floating around her shoulders. Notwithstanding the width of the cloak, the rhythmical swing of her body and the youthfulness of her figure were revealed. The officer kept behind her and walked along with an absent-minded air, twirling his stick, like a man taking an aimless stroll. At this moment there was nobody in sight, in that part of the street, except him and her. But, just after she had crossed the Avenue Marceau and some time before he reached it, a motor standing in the avenue started driving in the same direction as the nurse, at a fixed distance from her. It was a taxi-cab. And the officer noticed two things: first, that there were two men inside it and, next, that one of them leant out of the window almost the whole time, talking to the driver. He was able to catch a momentary glimpse of this man's face, cut in half by a heavy mustache and surmounted by a gray felt hat.