By-and-by the mystery deepened.  In a recess close to the top of the flight of stairs that led to the black door was an old-fashioned case clock.  When this clock struck the hour, two small mechanical figures dressed like German burghers of the sixteenth century came out of two little turrets, bowed gravely to each other, and then retired, like court functionaries, backwards.  It was a source of great pleasure to me to watch these figures go through their hourly pantomime But after a time it came into my head to wonder whether they did their duty by night as well as by day; whether they came out and bowed to each other in the dark, or waited quietly in their turrets till morning.  In pursuance of this inquiry, I got out of bed one night after Dance had left me, and relighted my candle.  I knew that it was just on the stroke of eleven, and here was a capital opportunity for studying the customs of my little burghers by night.  I stole up the staircase with my candle, and waited for the clock to strike.  It struck, and out came the little figures as usual.

“Perhaps they only came because they saw my light,” I said to myself.  I felt that the question as to their mode of procedure in the dark was still an unsettled one.

But scarcely had the clock finished striking when I was disturbed by the shutting of a door downstairs.  Fearing that someone was coming, and that the light might betray me, I blew out my candle and waited to hear more.  But all was silent in the house.  I turned to go down, but as I did so, I saw with astonishment that a thin streak of light shone from under the black door.  I stood like one petrified.  Was there anyone inside the room?  Listening intently, I waited for full five minutes without stirring a limb.  Silence the most profound upstairs and down.  Stepping on tiptoe, I went back to my room, shut myself in, and crept gladly into bed.

Next night my curiosity overmastered my fear.  As soon as Dance was gone I crept upstairs in the dark.  One peep was enough.  As on the previous night, a thin streak of light shone from under the black door—­evidence that it was lighted up inside.  Next night, and for several nights afterwards, I put the same plan in operation with precisely the same result.  The light was always there.

Having my attention thus concentrated as it were upon this one room, and lying awake so many hours when I ought to have been asleep, my suspicions gradually merged into certainty that it was visited every midnight by someone who came and went so lightly and quietly that only by intently listening could I distinguish the exact moment of their passing my door.  Who was this visitor that came and went so mysteriously?  To discover this, without being myself discovered, was a matter that required both tact and courage, but it was one on which I was almost as much a monomaniac as a child well can be.  To have opened my door when the landing was perfectly dark would have been