After Sir Rowland departs, Lady Wishfort rethinks the letter and decides a plot must be afoot. She insults and abuses Foible, who still tries to save the plan. She fails, however, and Lady Wishfort threatens to bring the law down upon her and Waitwell. Mrs. Fainall assures Foible that Mirabell is hurrying to bail Waitwell out of jail, but she laments that her affair with Mirabell will come out. Foible, in turn, assures Mrs. Fainall that she has evidence against Marwood of her infidelities, and they are willing to talk.

For her part, Millamant says she will marry Sir Wilfull rather than lose half her fortune. Lady Wishfort and Marwood join Mrs. Fainall, and Lady Wishfort chastises her daughter for her misconduct severely. Mrs. Fainall claims that all the accusations against her are false and makes some of her claims against Marwood.

This is enough to make Lady Wishfort doubt. After all, she has educated her daughter very carefully, she muses, not letting her be around men for years. Marwood, however, reminds her of the dangers of the accusations themselves, especially the possibilities of embarrassing legal difficulties and court sessions. The Lady is horrified and decides to “give up all”—her fortune, her niece, and even herself—to avoid such horrors.

Fainall arrives and makes demands of Lady Wishfort. She is not to marry without his consent, and he will take control of his wife’s money and the half of Millamant’s fortune at stake—especially since Millamant has now made a contract with Mirabell against her aunt’s wishes. The Lady asks for “time to consider,” to which Fainall grants her only the time it takes to draw up an official document.

When Fainall leaves, Lady Wishfort laments, “Must I be subject to this merciless villain?” Marwood reminds her that her own daughter’s “wantonness” is at fault. Millamant enters with Sir Wilfull and tells her aunt she will consent to marry him. Mirabell then arrives and seconds the offer, although the Lady does not trust him.

Fainall returns with the document and refuses to relent even when he hears of Millamant’s proposed marriage to Sir Wilfull. He still holds the card of Mrs. Fainall’s infidelity and the embarrassment that could come from its public exposition. Mirabell suggests that there is something else he can do but hesitates since Lady Wishfort has already “disposed of her [Millamant] who only could have made me a compensation for all my services.” Still, he decides to help.

At this point, Foible steps forward with their accusation against Marwood. Waitwell appears with the black box of papers, and Mirabell pulls out a surprise. It turns out that Mrs. Fainall put her fortune into a trust guarded by Mirabell, so Fainall has no claim at all to it. He vows revenge, but Mirabell assures the others that there is nothing much he can do.

Lady Wishfort is now so grateful that she agrees to allow Millamant and Mirabell to marry. Sir Wilfull gladly renounces his claim, saying: “I have no mind to marry.” Mirabell restores the trust to Mrs. Fainall, making her and her mother independent and able to “live easily together.”