Possessed by the belief that her sister, either alive or dead, was hidden somewhere inside the Hall, poor Susan, as we already know, whenever she could escape her mother's vigilance, took to wandering about the grounds in the dusk of evening, gazing up at the windows of the old house, more especially at her sister's bedroom window, often fancying that she heard Katherine's voice calling her, and trying everywhere to find some traces of the missing girl. After a time the thought seemed to have entered her head that if she could only get inside the Hall and search there, it would be better still. It would appear that on two occasions during Katherine's service there, when Susan had gone up to the Hall hoping to see her sister, Aaron Stone had locked up for the night. Susan had then thrown some pieces of gravel at her sister's window, in order to attract attention; upon which Katherine had come out to her, kissed her, and bidden her to return home. Susan, curious to know by what means her sister had been able to leave the house after it was made safe for the night, had persuaded Katherine to tell her. Among other rooms on the ground-floor at the back of the Hall, or rather at its side, and the side not frequented, was one that was called the wood-room, in which logs were kept to dry for winter burning. The unglazed window of this room was protected by horizontal iron bars; and one day, by a mere accident, Katherine saw that the lowest bar was loose in its socket; it could be displaced and replaced at will, and there was not the smallest difficulty in stepping through the low aperture to the ground outside. Katherine had thought it no harm to make use of this discovered means of egress on the one or two occasions she had seen her poor simple sister waiting, rather than let the girl remain there, as she might have done, for half the nights When the loss came, poor Susan never spoke of this, lest it might bring blame on Katherine's memory. But she did not forget it. And when, impelled by uncontrollable longing to discover a clue to her sister's fate and to venture inside the house, she sought for the window, she readily found it. She had but to displace the bar, step in, and be within the Hall. Near the door of the wood-room was a narrow, back staircase, hardly ever used, which led up to the north wing, and so to the bedroom which Katherine had occupied.