Liddy brought me some tea while I rested after my trip, and on the tray was a small book from the Casanova library.  It was called The Unseen World and had a cheerful cover on which a half-dozen sheeted figures linked hands around a headstone.

At this point in my story, Halsey always says:  “Trust a woman to add two and two together, and make six.”  To which I retort that if two and two plus X make six, then to discover the unknown quantity is the simplest thing in the world.  That a houseful of detectives missed it entirely was because they were busy trying to prove that two and two make four.

The depression due to my visit to the hospital left me at the prospect of seeing Halsey again that night.  It was about five o’clock when Liddy left me for a nap before dinner, having put me into a gray silk dressing-gown and a pair of slippers.  I listened to her retreating footsteps, and as soon as she was safely below stairs, I went up to the trunk-room.  The place had not been disturbed, and I proceeded at once to try to discover the entrance to the hidden room.  The openings on either side, as I have said, showed nothing but perhaps three feet of brick wall.

There was no sign of an entrance—­no levers, no hinges, to give a hint.  Either the mantel or the roof, I decided, and after a half-hour at the mantel, productive of absolutely no result, I decided to try the roof.

I am not fond of a height.  The few occasions on which I have climbed a step-ladder have always left me dizzy and weak in the knees.  The top of the Washington monument is as impossible to me as the elevation of the presidential chair.  And yet—­I climbed out on to the Sunnyside roof without a second’s hesitation.  Like a dog on a scent, like my bearskin progenitor, with his spear and his wild boar, to me now there was the lust of the chase, the frenzy of pursuit, the dust of battle.  I got quite a little of the latter on me as I climbed from the unfinished ball-room out through a window to the roof of the east wing of the building, which was only two stories in height.

Once out there, access to the top of the main building was rendered easy—­at least it looked easy—­by a small vertical iron ladder, fastened to the wall outside of the ball-room, and perhaps twelve feet high.  The twelve feet looked short from below, but they were difficult to climb.  I gathered my silk gown around me, and succeeded finally in making the top of the ladder.

Once there, however, I was completely out of breath.  I sat down, my feet on the top rung, and put my hair pins in more securely, while the wind bellowed my dressing-gown out like a sail.  I had torn a great strip of the silk loose, and now I ruthlessly finished the destruction of my gown by jerking it free and tying it around my head.

From far below the smallest sounds came up with peculiar distinctness.  I could hear the paper boy whistling down the drive, and I heard something else.  I heard the thud of a stone, and a spit, followed by a long and startled meiou from Beulah.  I forgot my fear of a height, and advanced boldly almost to the edge of the roof.