She stepped up to the nearest door, and gave a summons with the knocker.
This door was Barfoot's.

She knew that; in the first instant of fear occasioned by the workman's approach, she had glanced at the door and reminded herself that here Mr.Barfoot dwelt, immediately beneath Bevis.

But for the wild alarm due to her conscience-stricken state she could not have risked the possibility of the tenant being still at home; and yet it seemed to her that she was doing the only thing possible under the circumstances.

For this woman whom she heard just above might perchance be one of Bevis's sisters, returned to London for some purpose or other, and in that case she preferred being seen at Barfoot's door to detection as she made for her lover's.
Uncertainty on this point lasted but a few seconds.

Dreading to look at the woman, Monica yet did so, just as she passed, and beheld the face of a perfect stranger.