The inspector at once sent off a constable, who, with Constable Baker, the man on the Hambledon Road beat at the time, went to No. 14. Their knock was not answered very promptly. A servant came to the door, still fidgeting with her cap and apron, as though she had put them on hastily, and she gave a start when she saw the policeman. She said her mistress--a Mrs. Fitzroy--was at home, but she seemed a little reluctant to let the officers walk into the dining-room without a preliminary announcement, which was only natural, perhaps. They entered to find the room empty. Mrs. Fitzroy was not in the house. The servant knew nothing about the telephone call. She said it was her night out, that she had come in by the back door, as usual, and was upstairs taking off her hat and jacket when the policeman knocked. This was the outline of the mystery which I gave to Christopher Quarles as we walked from Kew Gardens Railway Station to Hambledon Road. The investigation had only been placed in my hands that morning, and I knew no details myself. "Shall we find Constable Baker at the house?" he asked presently. "Yes; I have arranged that," I answered. The house was a fair size, semi-detached, with half a dozen steps up to the front door, and it had a basement. There was a small window on the right of the door which gave light to a wide passage hall, and on the other side was the large window of the dining-room. Baker opened the door for us. "No news of Mrs. Fitzroy?" I asked. "None, sir." He was a smart man. I had worked with him before. "What time was it when you entered the house last night?" asked Quarles. "Ten o'clock, sir. A clock struck while we were standing on the steps." "Was the light burning in the hall and in the dining-room?" "Yes, sir; full on." "And the dining-room door was shut?" "Yes, sir." "You searched the house for Mrs. Fitzroy?" "We did. Have you just come from the police station?" "No." "I have reported one or two points," said Baker. "The gardens of these houses all have a door opening onto a footpath, on the other side of which there is a tennis club ground. "The path ends in a blank wall at one end; the other end comes out into Melbury Avenue, a road running at right angles to Hambledon Road. I found the garden gate here unbolted, and the servant, Emma Lewis, says she has never known it to be unfastened before. Also in Melbury Avenue last evening I saw a taxi waiting. I saw it first at about eight o'clock, and it was still there at a quarter past nine, when I spoke to the driver. He said he had brought a gentleman down, who had told him to wait there, and had then walked up Melbury Avenue. It was not the first time he had driven him to the avenue, and the driver supposed it was a clandestine love affair. After we found that Mrs. Fitzroy was missing, I went to look for the taxi. It had gone. I had noticed the number, however, and they are making inquiries at the police station."