Half-past twelve was striking as I came out of the terminus, buttoning up my overcoat, and pulling my soft hat firmly down upon my head, started to walk to Hyde Park Corner.  
I had declined the services of the several taxi-drivers who had accosted me and had determined to walk a part of the distance homeward, in order to check the fever of excitement which consumed me.
 
Already I was ashamed of the strange fears which had been mine during the journey, but I wanted to reflect, to conquer my mood, and the midnight solitude of the land of Squares which lay between me and Hyde Park appealed quite irresistibly.
 
There is a distinct pleasure to be derived from a solitary walk through London, in the small hours of an April morning, provided one is so situated as to be capable of enjoying it. To appreciate the solitude and mystery of the sleeping city, a certain sense of prosperity—a knowledge that one is immune from the necessity of being abroad at that hour—is requisite. The tramp, the night policeman and the coffee-stall keeper know more of London by night than most people—but of the romance of the dark hours they know little. Romance succumbs before necessity.
 
I had good reason to be keenly alive to the aroma of mystery which pervades the most commonplace thoroughfare after the hum of the traffic has subsided—when the rare pedestrian and the rarer cab alone traverse the deserted highway. With more intimate cares seeking to claim my mind, it was good to tramp along the echoing, empty streets and to indulge in imaginative speculation regarding the strange things that night must shroud in every big city. I have known the solitude of deserts, but the solitude of London is equally fascinating.
 
He whose business or pleasure had led him to traverse the route which was mine on this memorable night must have observed how each of the squares composing that residential chain which links the outer with the inner Society has a popular and an exclusive side. The angle used by vehicular traffic in crossing the square from corner to corner invariably is rich in a crop of black board bearing house-agent's announcements.
 
In the shadow of such a board I paused, taking out my case an leisurely selecting a cigar. So many of the houses in the southwest angle were unoccupied, that I found myself taking quite an interest in one a little way ahead; from the hall door and from the long conservatory over the porch light streamed out.
 
Excepting these illuminations, there was no light elsewhere in the square to show which houses were inhabited and which vacant. I might have stood in a street of Pompeii or Thebes—a street of the dead past. I permitted my imagination to dwell upon this idea as I fumbled for matches and gazed about me. I wondered if a day would come when some savant of a future land, in a future age, should stand where I stood and endeavor to reconstruct, from the crumbling ruins, this typical London square. A slight breeze set the hatchet-board creaking above my head, as I held my gloved hands about the pine-vesta.
 
At that moment some one or something whistled close beside me!
 
I turned, in a flash, dropping the match upon the pavement. There was no lamp near the spot whereat I stood, and the gateway and porch of the deserted residence seemed to be empty. I stood there peering in the direction from which the mysterious whistle had come.
 
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 n............