Mrs. Cheveley and Lord Goring confront each other, the former having come to trade Sir Robert's letter for Goring's hand in marriage. Their conversation reveals that during their courtship many years ago, Mrs. Cheveley seduced Goring to swindle him for a settlement. Now, however, Cheveley declares that Goring is the only man she has ever cared for. In any case, Goring refuses harshly.
Cheveley reasserts her intention to ruin Sir Robert, justifying her scheme as a mercenary transaction; Goring accuses her of defiling a sacred love, an act for which there can be no forgiveness. Coyly defending herself, Mrs. Cheveley protests that she only came to expose Sir Robert while visiting the Chilterns to retrieve her brooch. Goring then casually retrieves the bracelet from his writing table and, informing her that it can only be worn as a bracelet, suddenly clasps it on her arm. Calmly he reveals that he gave the brooch/bracelet years ago to a cousin as a wedding present and now knows that Mrs. Cheveley was guilty of its theft. Claiming that he has heard her confession, he will deliver her to the police unless she gives him Sir Robert's letter. Desperately, Mrs. Cheveley tries to rip the handcuff from her arm; Goring taunts that she cannot without releasing its secret spring.
Fearing arrest, Mrs. Cheveley surrenders the letter. As Goring burns it, she catches sight of Lady Chiltern's letter on the writing table. Asking Goring for a glass of water, she snatches the letter and puts it in her pocket. She then announces to Lord Goring that Gertrude's confession of love to her paramour has come into her hands. As her final act of vengeance, she plans to send it— misconstrued as a love letter addressed to Goring—to Sir Robert immediately. Goring moves to wrest it from her, with force if necessary; Mrs. Cheveley rings the bell and triumphantly has Phipps show her out. The act ends with Goring alone, lighting a cigarette and biting his lip.
In some sense the play's climatic moment, the face-off between An Ideal Husband's most active characters—Mrs. Cheveley and Lord Goring—is particularly rich. We will consider it in three parts. Continuing with the theme of marriage, we will first examine Mrs. Cheveley's attitudes toward courtship and conjugal life. Second, we will take up Mrs. Cheveley's unmasking as a "monster" and Goring's relation to the feminine. Finally, we will briefly consider the various objects that change hands in the course of this showdown.
It is in this scene, with her proposal to Goring, that Mrs. Cheveley—to use Lord Goring's term—most explicitly defiles married life. Already we know that she has ruthlessly wreaked havoc in the Chilterns' household; we now learn that she swindled Goring with a false courtship in their youth. Thus Mrs. Cheveley offers a condensed version of her philosophy of marriage in a clever epigram: "Romance should never begin with sentiment. It should begin with science and end with a settlement." Ever the opportunist, Cheveley would thus substitute the "settlement"—that is, financial gain—for romance's "sentiment." Accordingly, she makes her proposal to Goring a vulgar transaction, offering to trade Sir Robert's letter for his hand. At the same time, whether Cheveley truly still loves Goring is unclear: her uncharacteristic pauses after Goring's insults remain ambiguous.
Notably, Act III avenges these crimes against marriage through the diamond brooch. Revealed as a wedding gift Mrs. Cheveley stole in her youth, the brooch returns as evidence of a past crime, entrapping a woman who would manipulate another's past wrongs to her own advantage and ruin his conjugal bliss. The poetic justice in her arrest is clear.
Along with staging this scene of revenge, Act III involves a case of mistaken identity—more precisely, the case of the woman behind the door. Indeed, one of the most ironic events in the act is that the villainness stands in the place of her foil, the consummately virtuous heroine. This confusion of women notwithstanding, however, it is here that the villainess will be definitively unmasked as a monster. Once trapped by Lord Goring, Cheveley dissolves into a "paroxysm of rage, with inarticulate sounds," her loss of speech giving way to an agony of terror that distorts her face. For a moment, a "mask has fallen," and Cheveley is "dreadful to look at." Her veneer of wit and beauty thus give way to a hidden beast.
Mrs. Cheveley's monstrosity is intimately related to what one might describe as her "bad" femininity, the femininity that belongs to the femme fatale. Whereas the play's "good woman"—a naive, candid, and earnest Lady Chiltern—embodies the virtues associated with womanliness, the witty and ambitious Mrs. Cheveley is characterized by what are conventionally considered feminine vices. Most notable is her duplicity. Throughout the play, Mrs. Cheveley appears as the product of "horrid combinations" that evoke her dangerous deceitfulness. In Act I, for example, Lady Basildon recoils from Mrs. Cheveley's "unnatural" union of daytime genius and nighttime beauty. Here the stage notes describe her as "lamia-like"—that is, part woman and part snake in her treacherous and deceptive nature. Lord Goring goes so far as to call her womanliness into question, remarking that for a fascinating woman such as her, sex is a challenge, not a defense. Mrs. Cheveley is aggressive and ambitious like a man; her sex is an obstacle to her desires. Horrid and unnatural, she is a monstrous woman.
Mrs. Cheveley's unmasking aside, the face-off between Goring and Cheveley also provides an opportunity to consider how the dandy might be associated with the notions of the feminine described here. Certainly the dandy is a figure of questionable masculinity, indeed often considered the paragon of the effeminate male. Lord Goring is no exception. In the previous section, we quoted Goring as declaring that "mothers are darlings," a remark that aligns him with women in familial life at least. His truer female double, however, is Mrs. Cheveley herself. Like Cheveley, Goring is artificial, amoral, cunning, duplicitous, irrational, and flamboyantly well dressed: all the traits associated with her dangerous and "unnatural" femininity. Goring is Mrs. Cheveley's only match because he can play her game of wiles. In light of Wilde's sodomy trials and interest in the homoerotic, one could speculate on how these motifs of unnatural and monstrous femininity that apply to the dandy might serve as ciphers for male effeminacy, gay or otherwise. As an additional observation in this vein, we might also note how Goring drops his "social face" in the encounter with his enemy. Strangely, at the end of the act, Goring, the consummate dandy-gentleman, will desperately threaten Cheveley with violence when she takes Lady Chiltern's letter. The usually cool Goring loses his sense of decorum, a loss that compromises his manliness even further.
Along with raising these gender issues, Act III also brings together the series of transactions that organize the play, transactions that involve three objects: Sir Robert's letter to Baron Arnheim, Mrs. Cheveley's diamond brooch, and Lady Chiltern's pink note to Lord Goring. In this scene, all pass through the hands of Mrs. Cheveley and Lord Goring at some point, once again emphasizing how the two are the play's most pivotal characters and positioning their face-off as the play's climax. As the "causes" of complication in the plot, it is fitting that all these objects emerge at the plot's most tense moment.
The central object of this encounter is of course the brooch/bracelet-turned-handcuff. As a symbol, it suggests numerous interpretations. A diamond snake, it is easily stands in for the evil woman, a skin-shedding villainness defined by duplicity and subterfuge. It is also a fitting weapon for our dandy-hero—that is, a luxury item that relies on guile rather than force and entraps its victim with style. This "wonderful"—or, in modern parlance, "fabulous"—ornament thus emblematizes the artistry and cunning of the dandy as much as it does the evil woman.