A gray-gowned woman at a masked ball entices wealthy society man Philip Greycourt, who is bored with easy conquests, to a hotel, and then leaves without having removed her mask. Later, Philip visits the country home of John Villiers with a friend, and although Philip thinks that Villiers' second wife Helen, who flirts with him, is the masked woman, she denies having met him earlier. Helen's stepdaughter Catherine falls in love with Philip, but he scarcely notices her. When Villiers leaves for town one evening, Helen invites Philip to her sitting room and admits that she was the masked woman. Villiers returns unexpectedly, and seeing shadows of figures in a window embracing, he runs inside. The maid warns Helen, and Philip enters another room where Catherine lies in bed. As Villiers pounds on the door, Catherine accepts Philip's proposal and they marry the next day. Later, after Villiers dies, Helen attempts to seduce Philip, and jealously tells Catherine, whom Philip now loves, of their past. When Philip learns that Catherine has left to board a steamer, he follows and they enjoy a honeymoon cruise.