"They left the house without being observed, and our reporter saw Sophy as far as St. Martin's Lane, and then bade her good night. Before returning to his chambers he walked in the direction of the Embankment with the intention of taking a stroll there. It was a favorite promenade of his on fine nights, and on this night in particular he desired it, in order that he might think in the quietude of that grand avenue of the information he had gained. Elated as he was at the progress he was making in the elucidation of the mystery, he could not but be conscious that every new discovery he had made seemed to add to its difficulty. What he wanted now was a tangible clew, however slight, which he could follow up in a practical way. Little did he dream that everything was working in his favor, and that time and circumstance were leading him to the clew he was so anxious to possess. "There was one thing in the story related to him by Sophy which greatly perplexed him. The child could not have assisted him to a satisfactory solution, for he was satisfied that she had disclosed all she knew of the events of the night, and he therefore had made no mention to her of the perplexing point. It was this. Sophy had told him that while she was sitting on the stairs with her eyes closed she heard the man unlock the street door and take the chain down. That being so, the question remained--how had he got into the house? Scarcely through the street door, for it was hardly likely that, having got in through it, he would have locked it and put the chain up, and thus created for himself a serious obstacle to his escape in the event of his being discovered before he had accomplished his work. Our reporter could think of no satisfactory answer to this question, and it had to take its place among other questions to which, in the present aspect of the case, no answers could be found. "He had turned on to the Embankment by way of Westminster Bridge, and passing under the arch of the Charing Cross Railway bridge, was proceeding onward toward Waterloo when he saw something that caused him to quicken his steps in its direction. Fate or chance was about to place in his hands the link for which he was yearning--a link but for which the mystery of M. Felix might forever have remained unravelled." CHAPTER XV. A SINGULAR ADVENTURE ON THE THAMES EMBANKMENT. "He saw before him, at a distance of some thirty yards, as nearly as he could judge, the figure of a woman standing upon the stone ramparts of the Embankment, close to Cleopatra's Needle. The light of a lamp was shining upon her form, which was stooping forward in the direction of the river.