She seemed to be decidedly satisfied with my personal appearance; talked to me on indifferent matters with great glibness; but suddenly became silent and diplomatic the moment I looked toward the stair and asked innocently if she had to go up and down them often in the course of the day.

As for the doctor himself he was unapproachable on the subject of the mysterious upper regions.

If I introduced chemistry in general into the conversation he begged me not to spoil his happy holiday hours with his daughter and me, by leading him back to his work-a-day thoughts.

If I referred to his own experiments in particular he always made a joke about being afraid of my chemical knowledge, and of my wishing to anticipate him in his discoveries.

In brief, after a week's run of the lower regions, the upper part of the red-brick house and the actual nature of its owner's occupations still remained impenetrable mysteries to me, pry, ponder, and question as I might.
Thinking of this on the river-bank, in connection with the distressing scene which I had just had with Alicia, I found that the mysterious obstacle at which she had hinted, the mysterious life led by her father, and the mysterious top of the house that had hitherto defied my curiosity, all three connected themselves in my mind as links of the same chain.