"She is one of the finest weapons in the enemy's armory, Petrie. But a woman is a two-edged sword, and treacherous. To our great good fortune, she has formed a sudden predilection, characteristically Oriental, for yourself. Oh, you may scoff, but it is evident. She was employed to get this letter placed in my hands. Give it to me." I did so. "She has succeeded. Smell." He held the envelope under my nose, and, with a sudden sense of nausea, I recognized the strange perfume. "You know what this presaged in Sir Crichton's case? Can you doubt any longer? She did not want you to share my fate, Petrie." "Smith," I said unsteadily, "I have followed your lead blindly in this horrible business and have not pressed for an explanation, but I must insist before I go one step farther upon knowing what it all means." "Just a few steps farther," he rejoined; "as far as a cab. We are hardly safe here. Oh, you need not fear shots or knives. The man whose servants are watching us now scorns to employ such clumsy, tell-tale weapons." Only three cabs were on the rank, and, as we entered the first, something hissed past my ear, missed both Smith and me by a miracle, and, passing over the roof of the taxi, presumably fell in the enclosed garden occupying the center of the square. "What was that?" I cried. "Get in--quickly!" Smith rapped back. "It was attempt number one! More than that I cannot say. Don't let the man hear. He has noticed nothing. Pull up the window on your side, Petrie, and look out behind. Good! We've started." The cab moved off with a metallic jerk, and I turned and looked back through the little window in the rear. "Someone has got into another cab. It is following ours, I think." Nayland Smith lay back and laughed unmirthfully. "Petrie," he said, "if I escape alive from this business I shall know that I bear a charmed life." I made no reply, as he pulled out the dilapidated pouch and filled his pipe. "You have asked me to explain matters," he continued, "and I will do so to the best of my ability. You no doubt wonder why a servant of the British Government, lately stationed in Burma, suddenly appears in London, in the character of a detective. I am here, Petrie--and I bear credentials from the very highest sources--because, quite by accident, I came upon a clew. Following it up, in the ordinary course of routine, I obtained evidence of the existence and malignant activity of a certain man. At the present stage of the case I should not be justified in terming him the emissary of an Eastern Power, but I may say that representations are shortly to be made to that Power's ambassador in London." He paused and glanced back towards the pursuing cab.