Two tea-time callers considerably upset Lady Windermere as she is happily preparing for her coming-of-age party that evening and admiring an unusual fan, the gift of her husband.
The first caller, the dashing Lord Darlington, intimates, hypothetically, that she should console herself with him because her husband is untrue to her; the second, the gossipy Duchess of Berwick, tells her bluntly that all London knows that Windermere is in the toils of a mysterious and fascinating Mrs. Erlynne.
Lord Darlington she dismisses with the observation that life is a sacrament; its ideal is love and its purification is sacrifice; and, she continues, because a husband is vile, should the wife be vile also? But the charge of the Duchess is supported when Lady Windermere finds, in a secret account book of her husband's, a record of large sums given to Mrs. Erlynne.
Later, Windermere, while not wholly explaining Mrs. Erlynne, tells his wife that he loves only her and their child, but he insists that she invite Mrs. Erlynne to her party. Mrs. Erlynne, he pleads, has atoned for a wrong of twenty years ago and seeks only to restore her place in society by being received by the scrupulously respectable Lady Windermere. Windermere, his appeal, refused, himself finally sends the invitation--in spite of his wife's threat to strike Mrs. Erlynne across the face with her fan.
Lady Windermere's courage fails when Mrs. Erlynne, "looking like an edition de luxe of a wicked French novel, meant specially for the English market," arrives and dominates the party. Lady Windermere takes refuge on the terrace with Darlington, who again pleads with her to leave Windermere and come to him. Rejected, he warns her that he is leaving England the following day.
Meanwhile, in the drawing-room, Mrs. Erlynne is informing Windermere that she is prepared to accept, next day, a proposal of marriage from Lord Augustus Lorton, an amiable but wealthy bore, one of the guests at the party. She demands of Windermere a considerable annual settlement as an additional attraction to Lorton. Mrs. Erlynne and Windermere leave for the terrace to discuss the matter further.
Lady Windermere, seeing them go out together, in a jealous rage writes a note to Windermere, then leaves for the apartment of Lord Darlington, resolved to accept his proposal. "It is he who has broken the bond of marriage," she decides. "I only break its bondage."
Mrs. Erlynne, returning alone to take leave of her hostess, is told by a servant that Lady Windermere has gone, leaving a letter. Mrs. Erlynne reads the letter and sinks into a chair, exclaiming: "Oh, how terrible! The same words that twenty years ago I wrote to her father, and how bitterly I have been punished for it! How can I save my child?"
She tells Windermere that his wife has retired with a headache and wishes him to say farewell to the guests. She induces Lord Augustus to take Windermere, on some pretext, to his club for the night, and then hastens to Darlington's rooms where Lady Windermere, now shaken by indecision, is awaiting him. Lady Windermere finally agrees to return to her husband, after Mrs. Erlynne, without revealing their relationship, pleads with her and promises to disappear from their lives forever.
As the women are about to leave, voices, including that of Lord Windermere, are heard outside. Mrs. Erlynne thrusts Lady Windermere behind a window curtain with the injunction to slip away at the first opportunity; she herself prepares to face the men; but, hearing also the voice of Lord Augustus, she hides in an adjoining room. The men enter. One of them soon notices a fan on the sofa. Windermere, recognizing it as his wife's, is about to search the rooms and is starting toward the stirring curtain when Mrs. Erlynne emerges dramatically. She diverts their attention, and Lady Windermere glides unnoticed from the room.
"I am afraid I took your wife's fan in mistake for my own when I was leaving your house," Mrs. Erlynne tells Windermere. Lord Augustus turns away as the other men smile.
The next morning, with Windermere still unaware of his wife's absence of the night before, Lady Windermere is gratefully pondering the self-sacrifice of Mrs. Erlynne. She is about to tell her husband of the whole incident when they are interrupted by delivery of the fan, accompanied by Mrs. Erlynne's card. Over her husband's protest, Lady Windermere instructs the butler to ask Mrs. Erlynne in.
Their visitor, casually apologizing for taking the fan, says that she is leaving at once for permanent residence abroad. "The English climate doesn't suit me," she tells them. "My ... heart is affected." She asks for photographs of Lady Windermere and her baby, and her hostess leaves to get them. Alone with Mrs. Erlynne, Windermere scornfully reproaches her, disclosing that she has been blackmailing him to protect his wife from the knowledge that the mother she had been told was dead had actually abandoned her for a lover, and now lives--a notorious divorcée--under the assumed name of Mrs. Erlynne. He taunts her cruelly with the scene of the night before in Darlington's home, and forbids her ever to see her daughter again.
Mrs. Erlynne replies: "Don't imagine I am going to have a pathetic scene with her and tell her who I am. I have no ambition to play the part of a mother, and why should I interfere with her illusions? I find it hard enough to keep my own. I lost one illusion last night. I thought I had no heart, but I find I have, and a heart doesn't suit me. Somehow it doesn't go with modern dress. I am going to pass entirely out of your lives. If you tell her, I shall make my name so infamous that it will mar every moment of her life."
Lady Windermere returns with the photographs and, alone for a moment with Mrs. Erlynne, promises, at the latter's insistence, that she will forever remain silent about her visit to Darlington's apartment. Mrs. Erlynne asks one more favor--the gift of the fan. She is about to go when Lord Augustus enters. In spite of his coldness, Mrs. Erlynne prevails upon him to see her to her cab. She leaves with a final meaningful glance at Lady Windermere.
A few moments later, Lord Augustus returns, bursting with joy. Mrs. Erlynne has "explained everything." The Windermeres are startled, but he tells them that Mrs. Erlynne had visited Darlington's rooms only in search of Lord Augustus in order to accept his proposal--provided he agrees that they shall leave England.
Lord Windermere says: "Well, you are marrying a very clever woman."
And Lady Windermere adds: "Ah, you're marrying a very good woman."