Before the play begins, a number of important events have taken place in the lives of the main characters, which Congreve reveals throughout the play. Arabella’s first husband, Languish, has died and left her his fortune. She begins a secret affair with Edward Mirabell. They end the affair and she gets married to a man Mirabell has selected (Fainall) because Mirabell is afraid that they will conceive a child out of wedlock (Congreve never explains why Mirabell just doesn’t marry her himself). Mirabell and Mrs. Arabella Fainall remain good friends after the affair ends.
Mirabell begins courting Mrs. Fainall’s cousin, Millamant, who lives with Millamant’s aunt and Mrs. Fainall’s mother, Lady Wishfort. To gain Wishfort’s favor for his marriage to Millamant, Mirabell flatters Wishfort and lavishes much attention on her. Wishfort becomes convinced that he loves her and falls for him. However, after Wishfort’s best friend, Mrs. Marwood, reveals what Mirabell was up to, her feelings for Mirabell change from love to hate. Now, she will not grant her permission for Mirabell to marry Millamant, an important problem because she controls Millamant’s £6,000 dowry.
The night before the first scene of the play, the first time Mirabell has gone back to Wishfort’s house since she found out his plan, Wishfort unceremoniously dismisses Mirabell from her “cabal night” club in front of Millamant, who doesn’t stand up for him, and a number of other people. Undiscouraged, Mirabell has already begun hatching a plan to coerce Wishfort into accepting the marriage, a plan that Millamant learns all about through Foible.
While all this is going on, Fainall has been having an affair with his wife’s and Lady Wishfort’s friend, Mrs. Marwood. Mirabell is the only one who suspects that this is going on. Foible and Mincing have witnessed the affair but have been sworn to secrecy by Marwood.
Unfolding in a single day, the play begins in the morning. Mirabell is waiting for word that his servant, Waitwell, and Wishfort’s servant, Foible, have gotten married according to his plan. In the meanwhile, he is playing cards with his enemy, Fainall. Mirabell hints that he knows that Fainall and Marwood are having an affair. But he also reveals to Fainall his love for both Millamant’s strengths and weaknesses of character. Hearing this, Fainall encourages him to marry her.
Later, the two men are joined by Witwoud and Petulant. Mirabell learns from the two that last night, Wishfort discussed her plan to marry Millamant off to his uncle, Sir Rowland, in order to disinherit Mirabell from his uncle’s fortune (we do not yet know that Sir Rowland isn’t a real person and that this is all actually part of Mirabell’s plan).
Mirabell’s plan is going well until Marwood, while hiding in a closet, overhears Mrs. Fainall and Foible discussing Mirabell’s entire plan and learns exactly what he’s up to. She shares this news with Fainall and they concoct a plan to ruin Mirabell and blackmail Wishfort.
That same afternoon at Wishfort’s house, Millamant also accepts Mirabell’s proposal and rejects the proposal of Sir Wilfull, whom Lady Wishfort wanted her to marry.
Together, Marwood and Fainall begin to counteract Mirabell’s plan. They reveal Foible’s betrayal and Sir Rowland’s true identity (Waitwell) to Wishfort, and Fainall has Waitwell arrested. He threatens Wishfort that unless she surrenders her fortune, including Millamant and Mrs. Fainall’s shares, he will reveal Mrs. Fainall’s affair with Mirabell to the town, which would bring great disgrace to her family. He also demands that Wishfort herself agree never to get married (unless he permits it).
Mrs. Wishfort thinks she has found a loophole in Fainall’s plan when she learns that Millamant and Sir Wilfull have agreed to get married. However, Fainall is undeterred because he can still gain control of Wishfort and her wife’s fortunes.
All seems lost for Wishfort and her family until Mirabell steps in. Before he offers his help, he has Wishfort promise that she will let him marry Millamant, which she readily does.
Then, he calls forward first Mincing and Foible to reveal the affair between Fainall and Mrs. Marwood. Wishfort is dissatisfied that this is Mirabell’s trump card but Mirabell has one more trick. He calls forward Waitwell, who brings with him a deed to all of Arabella Languish’s property. Before marrying Fainall, Mirabell and Arabella suspected that Fainall might try to cheat her, so Arabella agreed to sign over her fortune to Mirabell as a precaution. As her trustee, Mirabell still controls her fortune and the legally binding document thus preempts Fainall’s claim on his wife’s fortune.
With Fainall and Marwood beaten and Mrs. Fainall and Wishfort’s fortunes and reputations saved, Sir Wilfull releases Millamant from the engagement so she can marry Mirabell and he can continue with his plans to travel. Mirabell returns the deed to Arabella and tells her to use it to control a very upset and vengeful Fainall.