I paused in my work, leaning back wearily and wondering what detained Nayland Smith so late. Some friends from Burma had carried him off to a theater, and in their good company I had thought him safe enough; yet, with the omnipresent menace of Fu-Manchu hanging over our heads, always I doubted, always I feared, if my friend should chance to be delayed abroad at night. What a world of unreality was mine, in those days! Jostling, as I did, commonplace folk in commonplace surroundings, I yet knew myself removed from them, knew myself all but alone in my knowledge of the great and evil man, whose presence in England had diverted my life into these strange channels. But, despite of all my knowledge, and despite the infinitely greater knowledge and wider experience of Nayland Smith, what did I know, what did he know, of the strange organization called the Si-Fan, and of its most formidable member, Dr. Fu-Manchu? Where did the dreadful Chinaman hide, with his murderers, his poisons, and his nameless death agents? What roof in broad England sheltered Kâramaneh, the companion of my dreams, the desire of every waking hour? I uttered a sigh of despair, when, to my unbounded astonishment, there came a loud rap upon the window pane! Leaping up, I crossed to the window, threw it widely open and leant out, looking down into the court below. It was deserted. In no other window visible to me was any light to be seen, and no living thing moved in the shadows beneath. The clamor of Fleet Street's diminishing traffic came dimly to my ears; the last stroke from St. Paul's quivered through the night. What was the meaning of the sound which had disturbed me? Surely I could not have imagined it? Yet, right, left, above and below, from the cloisteresque shadows on the east of the court to the blank wall of the building on the west, no living thing stirred. Quietly, I reclosed the window, and stood by it for a moment listening. Nothing occurred, and I returned to the writing-table, puzzled but in no sense alarmed. I resumed the seemingly interminable record of the Si-Fan mysteries, and I had just taken up my pen, when ... two loud raps sounded upon the pane behind me. In a trice I was at the window, had thrown it open, and was craning out. Practical joking was not characteristic of Nayland Smith, and I knew of none other likely to take such a liberty. As before, the court below proved to be empty.... Some one was softly rapping at the door of the chambers! I turned swiftly from the open window; and now, came _fear_. Momentarily, the icy finger of panic touched me, for I thought myself invested upon all sides. Who could this late caller be, this midnight visitor who rapped, ghostly, in preference to ringing the bell?