A happy marriage is placed at risk when the husband starts spending his afternoons with a social climbing adventuress.

In London, in 1949, elderly Mrs. Erlynne is attending an auction when she recognizes one of the items being offered, a Regency period fan, as belonging to her. It had been in storage for many years and is being sold as unclaimed property from a blitzed building. The auctioneer informs Mrs. Erlynne that if she can find another party who can vouch that the fan is hers, she can have it. Anxious to reclaim the fan, Mrs. Erlynne goes to see Lord Robert Darlington, who does not remember her at first. To jog his memory, she tells him that she has seen the fan that once belonged to the now-deceased Lady Margaret Windermere, with whom Lord Darlington was very much in love. As they walk together, Mrs. Erlynne shows Lord Darlington where they first met, a shop that in 1899 was a jewelers called Warrington's. Mrs. Erlynne then recounts the day in 1899 when in desperation, she came to the shop to sell her earrings. While she is there, she overhears Lord Arthur Windermere, who is accompanied by Lord Darlington and their friend, Cecil Graham, ordering that a fan he has purchased for his wife be inscribed with her name and birthdate. After they leave, Mrs. Erlynne tells the jeweler that Lord Windermere gave him the wrong date for his wife's birthday. When Lord Windermere returns to confirm this, Mrs. Erlynne tells him that she knew the correct date from reading the newspaper society columns. Later that day, however, Margaret comments to her husband that there has been no mention of her upcoming birthday ball in the newspapers. Back in the present, Lord Darlington seeks refuge from Mrs. Erlynne at his tailors, but she invades the fitting room and continues her story: His curiosity piqued, Lord Windermere visits Mrs. Erlynne at her hotel, but she refuses to reveal how she knows his wife's birthdate and explains to him that she is trying to break into London society to find a husband. Later, Mrs. Erlynne is invited to a fencing tournament by Lord Augustus Lorton. Before the contest is interrupted by rain, Lord Darlington makes overtures to Margaret. Soon after the tournament, Lord Windermere learns that Mrs. Erlynne has leased a house in his name. When she informs him that she plans to become Lord Lorton's wife, Lord Windermere tells her that she is the most outrageously brazen woman he has ever met. Emboldened by rumors about Lord Windermere and Mrs. Erlynne, Lord Darlington continues attempts to seduce Lady Windermere. Eventually the Duchess of Berwick informs Lady Windermere of her husband's involvement with Mrs. Erlynne but she at first refuses to believe it. A doubt-filled Lady Windermere finally examines her husband's checkbook, where she discovers records of several payments to Mrs. Erlynne. Lord Windermere tries to explain that he has done nothing wrong, but Margaret swears to find a way to hurt him for what he has done. The next day, Lord Windermere tells Mrs. Erlynne that, due to all the gossip, she will have to leave London. However, while he is with Mrs. Erlynne, an invitation to the ball arrives from Margaret. Lord Windermere, knowing the true identity of Mrs. Erlynne, gives her a check for £10,000. Back in the present, Mrs. Erlynne reveals to Lord Darlington that Margaret was her daughter but Lord Windermere was the only one who knew her secret because in order to appear young, she could not admit to having a grown daughter. Mrs. Erlynne then continues her story: At the ball, after Mrs. Erlynne introduces herself to Lady Windermere, Lord Darlington tells Margaret that he is in love with her and wants her to leave with him. When Mrs. Erlynne dances with Lord Windermere, telling him that she has practically snared Lord Lorton, Lady Windermere leaves the ball and goes alone to Lord Darlington's house. Mrs. Erlynne follows her and advises her to go back to her husband, assuring her that Lord Windermere has been writing checks on behalf of Lord Lorton, who has been trying to conceal his relationship with Mrs. Erlynne from his sister, the Duchess of Berwick. When Lord Darlington returns home with Lord Windermere, Lord Lorton and Cecil Graham for a drink, the women hide. The men soon discover Margaret's fan, and Lord Windermere accuses Lord Darlington of having an affair with his wife. Margaret escapes and Mrs. Erlynne claims the fan is hers, thus implicating herself in an affair with Lord Darlington and ruining her prospects with Lord Lorton. The next morning, Lady Windermere goes to visit Mrs. Erlynne to thank her for her sacrifice and Mrs. Erlynne says that she can repay her by being silent. After telling Mrs. Erlynne that her father died of a broken heart after her mother "died," Margaret leaves without discovering that Mrs. Erlynne is her mother. Mrs. Erlynne decides to stay in London and tears up the check Lord Windermere gave her. Later, Margaret sends her a bouquet of roses and the fan. Back at the tailors' shop, Lord Darlington invites Mrs. Erlynne to dine with him, and they leave to collect the fan from the auction house.