The drone of a taxicab, approaching from the north, increased in volume, as the vehicle came spinning around the angle of the square, passed me, and went droning on its way. I watched it swing around the distant corner ... and, in the new stillness, the whistle was repeated! This time the sound chilled me. The whistle was pitched in a curious, inhuman key, and it possessed a mocking note that was strangely uncanny. Listening intently and peering towards the porch of the empty house, I struck a second match, pushed the iron gate open and made for the steps, sheltering the feeble flame with upraised hand. As I did so, the whistle was again repeated, but from some spot further away, to the left of the porch, and from low down upon the ground. Just as I glimpsed something moving under the lee of the porch, the match was blown out, for I was hampered by the handbag which I carried. Thus reminded of its presence, however, I recollected that my pocket-lamp was in it. Quickly opening the bag, I took out the lamp, and, passing around the corner of the steps, directed a ray of light into the narrow passage which communicated with the rear of the building. Half-way along the passage, looking back at me over its shoulder, and whistling angrily, was a little marmoset! I pulled up as sharply as though the point of a sword had been held at my throat. One marmoset is sufficiently like another to deceive the ordinary observer, but unless I was permitting a not unnatural prejudice to influence my opinion, this particular specimen was the pet of Dr. Fu-Manchu! Excitement, not untinged with fear, began to grow up within me. Hyde Park was no far cry, this was near to the heart of social London; yet, somewhere close at hand, it might be, watching me as I stood--lurked, perhaps, the great and evil being who dreamed of overthrowing the entire white race! With a grotesque grimace and a final, chattering whistle, the little creature leapt away out of the beam of light cast by my lamp. Its sudden disappearance brought me to my senses and reminded me of my plain duty. I set off along the passage briskly, arrived at a small, square yard ... and was just in time to see the ape leap into a well-like opening before a basement window. I stepped to the brink, directing the light down into the well. I saw a collection of rotten leaves, waste paper, and miscellaneous rubbish--but the marmoset was not visible. Then I perceived that practically all the glass in the window had been broken. A sound of shrill chattering reached me from the blackness of the underground apartment. Again I hesitated. What did the darkness mask? The note of a distant motor-horn rose clearly above the vague throbbing which is the only silence known to the town-dweller. Gripping the unlighted cigar between my teeth, I placed my bag upon the ground and dropped into the well before the broken window. To raise the sash was a simple matter, and, having accomplished it, I inspected the room within.