A shadowy figure uprose, and vaguely I made it out for that of a man in the unobtrusive blue serge which is the undress uniform of the Force. "Well?" rapped my companion. "Mr. Slattin returned ten minutes ago, sir," reported the constable. "He came in a cab which he dismissed--" "He has not left again?" "A few minutes after his return," the man continued, "another cab came up, and a lady alighted." "A lady!" "The same, sir, that has called upon him before." "Smith!" I whispered, plucking at his arm--"is it--?" He half turned, nodding his head; and my heart began to throb foolishly. For now the manner of Slattin's campaign suddenly was revealed to me. In our operations against the Chinese murder-group two years before, we had had an ally in the enemy's camp--Karamaneh, the beautiful slave, whose presence in those happenings of the past had coloured the sometimes sordid drama with the opulence of old Arabia; who had seemed a fitting figure for the romances of Bagdad during the Caliphate--Karamaneh, whom I had thought sincere, whose inscrutable Eastern soul I had presumed, fatuously, to have laid bare and analysed. Now once again she was plying her old trade of go-between; professing to reveal the secrets of Dr. Fu-Manchu, and all the time--I could not doubt it--inveigling men into the net of this awful fisher. Yesterday, I had been her dupe; yesterday, I had rejoiced in my captivity. To-day, I was not the favoured one; to-day I had not been selected recipient of her confidences--confidences sweet, seductive, deadly: but Abel Slattin, a plausible rogue, who, in justice, should be immured in Sing Sing, was chosen out, was enslaved by those lovely mysterious eyes, was taking to his soul the lies which fell from those perfect lips, triumphant in a conquest that must end in his undoing; deeming, poor fool, that for love of him this pearl of the Orient was about to betray her master, to resign herself a prize to the victor! Companioned by these bitter reflections, I had lost the remainder of the conversation between Nayland Smith and the police officer; now, casting off the succubus memory which threatened to obsess me, I put forth a giant mental effort to purge my mind of this uncleanness, and became again an active participant in the campaign against the Master--the director of all things noxious. Our plans being evidently complete, Smith seized my arm, and I found myself again out upon the avenue. He led me across the road and into the gate of a house almost opposite. From the fact that two upper windows were illuminated, I adduced that the servants were retiring; the other windows were in darkness, except for one on the ground floor to the extreme left of the building, through the lowered venetian blinds whereof streaks of light shone out. "Slattin's study!" whispered Smith. "He does not anticipate surveillance, and you will note that the window is wide open!"