Suddenly she desisted, looking nervously at the open windows; then, crossing the room, she drew the curtains. I crept out into the road again and by the same roundabout route came back to the empty house. Feeling my way in the darkness of the shrubbery, I found the motor bicycle which I had hidden there and I wheeled it down to the further gate of the drive and waited. I could see the doctor's door, and I saw him returning along the road. As he appeared, from somewhere---I could not determine from where--came a strange and uncanny wailing sound, a sound that chilled me like an evil omen. Even as it died away, and before Dr. Stuart had reached his door I knew what it portended--that horrible wail. Some one hidden I knew not where, had warned Zara el-Khala that the doctor returned! But stay! Perhaps that some one was the dark-skinned chauffeur! How I congratulated myself upon the precautions which I had taken to escape observation. Evidently the watcher had placed himself somewhere where he could command a view of the front door and the road. Five minutes later the girl came out, the old housekeeper accompanying her to the door. The car emerged from the lane, Zara el-Khala entered it and was driven away. I could see no one seated beside the chauffeur. I started my "Indian" and leapt in pursuit. As I had anticipated, the route was Eastward, and I found myself traversing familiar ground. From the south-west to the east of London whirled the big car of mystery--and I was ever close behind it. Sometimes, in the crowded streets, I lost sight of my quarry for a time, but always I caught up again, and at last I found myself whirling along Commercial Road and not fifty yards behind the car. Just by the canal bridge a drunken sailor lurched out in front of my wheel, and only by twisting perilously right into a turning called, I believe, Salmon Lane, did I avoid running him down. _Sacre nom!_ how I cursed him! The lane was too narrow for me to turn and I was compelled to dismount and to wheel my "Indian" back to the highroad. The yellow car had vanished, of course, but I took it for granted that it had followed the main road. At a dangerous speed, pursued by execrations from the sailor and all his friends, I set off east once more turning to the right down West India Dock Road. Arriving at the dock, and seeing nothing ahead of me but desolation and ships' masts, I knew that that inebriated pig had spoiled everything! I could have sat down upon the dirty pavement and wept, so mortified was I! For if Zara el-Khala had secured the envelope I had missed my only chance. However, _pardieu!_ I have said that despair is not permitted by the Bureau. I rode home to my hotel, deep in reflection. Whether the girl had the envelope or not, at least she had escaped detection by the doctor; therefore if she had failed she would try again. I could sleep in peace until the morrow.