To what might not those doors lead?
In support of the plausibility of this conjecture, it further occurred to her that the forbidden gallery, in which lay the apartments of the unfortunate Mrs.Tilney, must be, as certainly as her memory could guide her, exactly over this suspected range of cells, and the staircase by the side of those apartments of which she had caught a transient glimpse, communicating by some secret means with those cells, might well have favoured the barbarous proceedings of her husband.

Down that staircase she had perhaps been conveyed in a state of well-prepared insensibility! Catherine sometimes started at the boldness of her own surmises, and sometimes hoped or feared that she had gone too far; but they were supported by such appearances as made their dismissal impossible.
The side of the quadrangle, in which she supposed the guilty scene to be acting, being, according to her belief, just opposite her own, it struck her that, if judiciously watched, some rays of light from the general's lamp might glimmer through the lower windows, as he passed to the prison of his wife; and, twice before she stepped into bed, she stole gently from her room to the corresponding window in the gallery, to see if it appeared; but all abroad was dark, and it must yet be too early.

The various ascending noises convinced her that the servants must still be up.

Till midnight, she supposed it would be in vain to watch; but then, when the clock had struck twelve, and all was quiet, she would, if not quite appalled by darkness, steal out and look once more.

The clock struck twelve--and Catherine had been half an hour asleep..