My obvious course, at such a time, would have been to wait for a patrolman or to slip quietly away and send word in to police headquarters. But, as I have already said, no man is wholly sane after midnight. Subliminal faculties, ancestral perversions, dormant and wayward tendencies, all come to the surface, emerging like rats about a sleeping mansion. And crowning these, again, was my own neurasthenic craving for activity, my hunger for the narcotizing influence of excitement. And it has its zest of novelty, this stepping into an unknown and unlighted house at three o'clock in the morning. That novelty takes on a razor-edge when you have fairly good evidence that some one who has no business there has already preceded you into that house. So as I stepped inside and quietly closed the door after me, I moved forward with the utmost care. Some precautionary sixth sense told me the place was not unoccupied. Yet the darkness that surrounded me was absolute. Not a sound or movement came to my ears as I stood there listening, minute after minute. So I crept deeper into the gloom. My knowledge of that stereotyped class of residence provided me with a very fair idea of where the stairway ought to stand. Yet it took much prodding and groping and pawing about before I came to it. One flicker of a match, I knew, would have revealed the whole thing to me. But to strike a light, under the circumstances, would be both foolish and dangerous. No house dog, I felt, would interrupt my progress; the mere remembrance of the intruder above me set my mind at rest on this point. I came to a stop at the head of the first stairway, puzzled by the completeness of the quiet which encompassed me. I directed my attention to each quarter of the compass, point by point. But I might have been locked and sealed in a cistern, so complete was the silence, so opaque was the blackness. Yet I felt that nothing was to be gained by staying where I was. So I groped and shuffled my way onward, rounding the banister and advancing step by step up the second stairway. This, I noticed, was both narrower and steeper than the first. I was also not unconscious of the fact that it was leading me into a zone of greater danger, for the floor I was approaching, I knew, would be the sleeping floor. I was half-way up the stairway when something undefined brought me to a sudden stop. Some nocturnal adeptness of instinct warned me of an imminent presence, of a menace that had not yet disclosed itself.