“I sat down to watch Baumgartner, his house,” replied Thrush. “The merit of those quiet little streets is that there are always apartments of sorts, though not always the most admirable sort, to be had in half the houses. There was quite a choice bang opposite Baumgartner’s, and I’d taken a front room before you were through Hammersmith. Of course I explained that I had lost a last train, and the landlady’s son embarrassed me with pyjamas of inadequate dimensions. Well, I sat at the front window all night, for no better reasons than my strong feeling about the doctor’s writings, and your daughter’s disbelief in his yarn about her brother. Soon after five in the morning the old bird came out, and I was after him like knife. I tracked him to Knightsbridge without much difficulty, excepting the one of avoiding being spotted, but there that happened by the merest accident. He was passing under the scaffolding outside the church they’re pulling down there, and he’s so tall he knocked his hat off. I admit I was too close. He saw, and must have recognised me; but I shouldn’t have recognised him if I hadn’t seen him start out. He was wearing a false beard and spectacles!” “That’s proof positive,” said ingenuous Mr. Upton, under his breath. “Well, I confess it’s something like it in this case; but it was a very awkward moment for me. I hadn’t to let him see I knew him, nor yet that I was following him, and the only way was to abandon the chase as openly as possible. It was then I decided that it was no use leaving poor old Mullins in pawn to the police. I redeemed him without delay. We went back to my new rooms together, which I needn’t tell you I liked so much that I brought a suit-case and took them for a week. Of course, as we had lost the run of Baumgartner, the next best thing was to watch for his return. Mullins took that on while I got some sleep; when I awoke the Park Lane murder was the latest, and I won’t say I didn’t suspect who’d done it. Perhaps I didn’t tell you he had his camera with him as well as beard and goggles, and all three figured in the first reports.” “But all this time you had no idea my boy was in the house?” “None whatever; we saw the girl once or twice, but that was all until I wired last night. What I never saw myself was Baumgartner’s return; but in the afternoon I sent Mullins round to another road to try and get a room overlooking the place from the back. Well, the houses were too much class for that; but one was empty, and he got the key and risked going back to prison for the cause! Suffice it that he set eyes on both man and boy before I sent that wire.” “And you left my son in that murderer’s clutches a minute longer than you could help?” It was a previous incarnation of Pocket’s father that broke in with this.