The clock below struck nine upon these meditations, and almost upon the last stroke I heard a sound that set my nerves tingling. I crouched in the dark waiting. Some one was coming toward me, but from where? The bottom of a well at midnight was not blacker than the fourth floor, but the switch lay ready to my hand, and my pockets were stuffed with matches of the sort that light anywhere. The stairways were all carpeted, as I have said, and yet some one was ascending bare treads, lightly, and with delays that suggested a furtive purpose. Meanwhile, as a background for this unreality, murmurs of talk and occasional laughter rose from the library. This concealed stairway, wherever it was, could not be of interminable length, and I had counted, I think, fifteen steps of that strange ascent when it ceased. I heard a fumbling as of some one seeking a latch, and suddenly a light current of air swept by me, but its clean fresh quality was not in itself disturbing. I stooped and struck a match smartly on the carpet and at the same time clicked the switch. I should say that not more than ten seconds passed from the moment the soft rush of air had first advertised the opening of a passage near me until the hall was flooded with the glow of the electric lamps overhead. My match had also performed its office, but finding the electric current behaving itself normally, I blew it out. What I saw now interested me immensely. In the solid wall, near the stair, and almost directly opposite the trunk-room, a narrow door had swung outward,--a neat contrivance, so light in its construction that it still swayed on its concealed hinges from the touch of the hand that had released it. How it had opened or what had become of the prowler who had unlatched it remained to be discovered. It seemed impossible that whoever or whatever had climbed the hidden stairway had descended, nor had I been conscious of a ghostly passing as on the previous night. I had only my senses to apply to this problem, and their efficiency was minimized for a moment by fear. The opening in the wall engaged my attention at once, and I was steadied by the thought that here was a practical matter susceptible of investigation. I stepped within the door and lighted a candle; and just as the wick caught fire, click went a switch somewhere, and out went the hall lamps. But having, so to speak, put my foot to the mysterious stair I would not turn back, and I continued on down the steps.