Flushed with apparent success, I looked up at the walls on either side of me.  They were gray with paint and presented one unbroken surface from base-board to ceiling, save where the two doorways opened, one into the library, the other into the dining-room.  Had the flying presence escaped by either of these two rooms?  I knew the dining-room well.  I had had several opportunities for studying its details.  I thought I knew the library; besides, Mr. Searles had been in the library when the shape advanced upon him from the hall,—­a fact eliminating that room as a possible source of approach!  What then was left?  The recess which had once served as an old-time entrance.  Ah, that gave promise of something.  It projected directly toward where the adjacent walls had once held two doors, between which any sort of mischief might take place.  Say that the Misses Quinlan had retained certain keys.  What easier than for one of them to enter the outer door, strike a light, open the inner one and flash this light up through the house till steps or voices warned her of an aroused family, when she had only to reclose the inside door, put out the light and escape by the outer one.

But alas! at this point I remembered that this, as well as all other outside doors, had invariably been protected by bolt, and that these bolts had never been found disturbed.  Veritably I was busying myself for nothing over this old vestibule.  Yet before I left it I gave it another glance; satisfied myself that its walls were solid; in fact, built of brick like the house.  This on two sides; the door occupied the third and showed the same unbroken coat of thick, old paint, its surface barely hidden by the cabinet placed at right angles to it.  Enough of it, however, remained exposed to view to give me an opportunity of admiring its sturdy panels and its old-fashioned lock.  The door was further secured by heavy pivoted bars extending from jamb to jamb.  An egg-and-dart molding extended all around the casing, where the inner door had once hung.  All solid, all very old-fashioned, but totally unsuggestive of any reasonable solution of the mystery I had vaguely hoped it to explain.  Was I mistaken in my theory, and must I look elsewhere for what I still honestly expected to find?  Undoubtedly; and with this decision I turned to leave the recess, when a sensation, of too peculiar a nature for me readily to understand it, caused me to stop short, and look down at my feet in an inquiring way and afterward to lift the rug on which I had been standing and take a look at the floor underneath.  It was covered with carpet, like the rest of the hall, but this did not disguise the fact that it sloped a trifle toward the outside wall.  Had not the idea been preposterous, I should have said that the weight of the cabinet had been too much for it, causing it to sag quite perceptibly at the base-board.  But this seemed too improbable to consider.  Old as the house was, it was not