The old woman was, of course, at home, but she was suspicious and alone.

He had some knowledge of her habits...

and once more he put his ear to the door.
Either his senses were peculiarly keen (which it is difficult to suppose), or the sound was really very distinct.

Anyway, he suddenly heard something like the cautious touch of a hand on the lock and the rustle of a skirt at the very door.

Someone was standing stealthily close to the lock and just as he was doing on the outside was secretly listening within, and seemed to have her ear to the door....