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.

The light showed a large kitchen, with torn wall-paper and decorator’s litter strewn about the floor, a whitewash pail in one corner, and nothing else.

I climbed in, and, taking from my pocket the Browning pistol without which I had never traveled since the return of the dreadful Chinaman to England, I crossed to the door, which was ajar, and looked out into the passage beyond.

Stifling an exclamation, I fell back a step.  Two gleaming eyes stared straightly into mine!

The next moment I had forced a laugh to my lips ... as the marmoset turned and went gamboling up the stairs.  The house was profoundly silent.  I crossed the passage and followed the creature, which now was proceeding, I thought, with more of a set purpose.

Out into a spacious and deserted hallway it led me, where my cautious footsteps echoed eerily, and ghostly faces seemed to peer down upon me from the galleries above.  I should have liked to have unbarred the street door, in order to have opened a safe line of retreat in the event of its being required, but the marmoset suddenly sprang up the main stairway at a great speed, and went racing around the gallery overhead toward the front of the house.