I was now fairly in the house, but the darkness was blacker than the pit, and I did not care to strike a match.  I felt my way along by the wall till I came to a door on the left; it was locked.  A little further was another door, also locked.  I listened intently, for I fancied I could hear a faint murmur of voices, but I was not sure.  Then I startled myself by stepping on nothing—­I was at the head of a flight of stone steps; down below I could distinguish an almost imperceptible glimmer of light.

“I’m in for it.  Here goes!” I reflected, and I crept down the steps one by one, and in due course reached the bottom.  To the left was a doorway, through which came the glimmer of light.  Passing through the doorway, I came into a room with a stone floor.  The light, which was no stronger than the very earliest intimation of a winter’s dawn, seemed to issue in a most unusual way from the far corner of this apartment near the ceiling.  I directed my course towards it, and in the transit made violent contact with some metallic object, which proved to be an upright iron shaft, perhaps three inches in diameter, running from floor to ceiling.

“Surely,” I thought, “this is the queerest room I was ever in.”

Circumnavigating the pillar, I reached the desired corner, and stood under the feeble source of light.  I could see now that in this corner the ceiling was higher than elsewhere, and that the light shone dimly from a perpendicular pane of glass which joined the two levels of the ceiling.  I also saw that there was a ledge about two feet from the floor, upon which a man would stand in order to look through the pane.

I climbed on to the ledge, and I looked.  To my astonishment, I had a full view of a large apartment, my head being even with the floor of that apartment.  Lying on a couch was a woman—­the woman who had accosted me on Dover Pier—­Carlotta Deschamps, in fact.  By her side, facing her in a chair, was Rosetta Rosa.  I could hear nothing, but by the movement of their lips I knew that these two were talking.  Rosa’s face was full of pity; as for Deschamps, her coarse features were inscrutable.  She had a certain pallor, but it was impossible to judge whether she was ill or well.

I had scarcely begun to observe the two women when I caught the sound of footsteps on the stone stair.  The footsteps approached; they entered the room where I was.  I made no sound.  Without any hesitation the footsteps arrived at my corner, and a pair of hands touched my legs.  Then I knew it was time to act.  Jumping down from the ledge, I clasped the intruder by the head, and we rolled over together, struggling.  But he was a short man, apparently stiff in the limbs, and in ten seconds or thereabouts I had him flat on his back, and my hand at his throat.

“Don’t move,” I advised him.

In that faint light I could not see him, so I struck a match, and held it over the man’s face.  We gazed at each other, breathing heavily.