Madame Gabrielle returned to Hereford Road to continue her watch. For my own part, I set to work, and very soon discovered that the mysterious house in Harrington Street was unoccupied and was to let furnished. In the guise of a possible tenant I went over it thoroughly, but could see nothing suspicious, except that I ascertained that the caretaker was an old compatriot of Heinrich's. The owner, who had left London and was now residing on the South Coast, was well known and his loyalty was beyond dispute. It then became evident that the caretaker was cognisant of the secret meeting, if, indeed, he was not closely concerned in the business, whatever it might be, that brought these men together in an empty house at dead of night so soon after a raid, when most honest people would be only too anxious to get to bed as promptly as possible. It was obviously necessary that we should learn all we could about the identity of the men who met in the empty house in Harrington Street, and I was soon in touch with the Special Branch, and made all the necessary arrangements for shadowing our suspects. Four nights later another raid took place. As soon as the Gothas were gone we were all swiftly at our posts. So thoroughly was the house surrounded that a mouse could hardly have gone in or out undetected. Yet there was no sign of a watcher, and anyone going to the house would certainly be in blissful ignorance of the fact that he was under the close scrutiny of the keen eyes of the Secret Service. There is very little clumsy "shadowing" about the Special Branch! But we watched in vain. No meeting was held, or if it was it was held elsewhere. The blind musician, it is true, left his room in Bayswater, but he never reached Harrington Street. The house remained all night silent and apparently deserted. I wondered whether the gang had by any chance discovered our activities and taken alarm. I was not very deeply concerned about it, apart from the chagrin which the delay caused me. Blind Heinrich, at any rate, could hardly escape us, and, if the gang had for any reason changed its place of meeting, I had little doubt that we should soon discover it. But who had blundered? I felt certain that it was not Madame Gabrielle, and I did not think it could be myself. One morning I received a note from the clever little Frenchwoman, asking me to take tea with her at Hereford Road that afternoon, and adding: "I have something to show you." Of course I went, and we had tea together in the big drawing-room which she used in common with the other guests in the boarding-house. Several of the old ladies who lived in the house were present. Just as we had finished our tea, Madame exclaimed: "Do excuse me, m'sieur! I have forgotten my handkerchief."