Lady Windermere strongly suspects her husband's relationship with Mrs. Erlynne when he asks her to invite the beautiful woman to her twenty-first-birthday ball. In fact, Mrs. Erlynne is Lady Windermere's divorced mother, whom Lord Windermere, without anyone's knowledge, is trying to help back into society.
When she arrives at the ball, Lady Windermere, in pique, goes
to the rooms of her admirer Lord Darlington. Mrs. Erlynne follows
her and has just persuaded her to leave when they are surprised
by the arrival of the men. They hide, but Lady Windermere forgets
her fan, which is immediately noticed. Mrs. Erlynne then saves
Lady Windermere from scandal by revealing herself, claiming the
fan, which she says she has borrowed, and letting her daughter
slip away unnoticed.