As the other guests go to dinner, Sir Robert and Mrs. Cheveley return to the Octagon room. Shifting their conversation to more practical subjects, Mrs. Cheveley raises the issue of an Argentine Canal scheme, a development fiasco in which she has heavily invested on the advice of their mutual friend: the recently deceased Baron Arnheim. Sir Robert is about to deliver the report of his special investigative commission to the House of Commons unmasking the affair; Mrs. Cheveley insists that he must not only withdraw the report but lend his support to the scheme as well or suffer the consequences. Mrs. Cheveley is blackmailing him.
Mrs. Cheveley's power over Sir Robert is her knowledge of the secret of his fortune's origins. As a young secretary, Sir Robert sold a Cabinet secret to Arnheim that enabled him to invest in the Suez Canal before the government announced its own purchase; Mrs. Cheveley holds the incriminating letter in her possession. Thus, after a few hopeless attempts at resistance, Sir Robert agrees to exchange his support for the piece of evidence.
Sir Robert then exits, and the guests return. Mrs. Cheveley triumphantly announces to Lady Chiltern that she has succeeded in winning her husband's support for the canal scheme; moreover, she and Sir Robert share a secret together. Sir Robert arrives and announces Mrs. Cheveley's carriage, and the latter then sails out on his arm.
In the following exchange, Mabel Chiltern, bantering with Lord Goring, comes upon a diamond brooch—shaped like a snake with a ruby on its head—on the sofa. Enigmatically, Goring insists that it is also a bracelet. Coolly he takes the brooch, puts it in a green letter case, and replaces the case in his breast pocket. He then asks Mabel to keep his possession of the brooch secret and inform him if anyone comes to claim it. Apparently, he gave it to someone many years ago.
Once all the guests have exited, Lady Chiltern confronts Sir Robert on the topic of the canal scheme. Though Sir Robert ambiguously protests he has only made a politically necessary compromise, Lady Chiltern demands that he write to Mrs. Cheveley, withdraw his support, and never see her again. She implores him to remain her ideal husband or else confess any secret disgraces from his past so that they may begin to drift apart. Unable to confess his crime, Sir Robert complies, and the two declare their love for each other. Lady Chiltern exits; Sir Robert commands Mason to put out the lights, leaving the chandelier illuminating the "Triumph of Love" in the background.
The second half of Act I introduces the play's primary theme—that of marriage—distributing a number of commentaries on married life among its various characters. We will begin with its heroes: the Chilterns.
This section of Act I drastically shifts the tone of the play, moving from the banter of the dinner party to the Chilterns' maudlin confrontation. While the transition from dinner party is gradual, the encounter between the Chilterns' is ultimately so different—in both length and style—from the dialogue thus far as to constitute a new melodramatic "mode" on stage. Note the devices that make up their exchange: Lady Chiltern's lyrical entreaty to her ideal husband ("Oh! Be that ideal still"), Sir Robert's near-confession when Lady Chiltern implores the latter to reveal any past disgraces, the dramatic irony produced when she declares the past the means by which one judges others, and the apparent doom foretold when Lady Chiltern sorrowfully declares that she and a husband who had deceived her would necessarily drift apart. These devices serve to raise the suspense and tension of the exchange; from a party of clever and ironic wits we have moved to an intimate scene between two characters overcome with emotion. Unlike Wilde's inimitable banter, this dialogue directly borrows from the conventions of the Victorian popular stage.
Thematically this exchange addresses ideals of marriage, love, and morality, introducing the notion of the ideal husband. Here the conventionally melodramatic dialogue serves as vehicle for a similarly generic discussion of love. Tellingly, this discussion describes love in explicitly gendered terms. As a woman, Lady Chiltern loves Sir Robert as an ideal husband, a man worthy of worship for the example he sets privately and publicly. As a result, she cannot accept Sir Robert's protestations regarding the need for practical compromises; she will have her ideal spouse or none at all. Sir Robert will confront his wife on the dangers of idealizing one's lover in the following act.
Act I also places a critique of Lady Chiltern's severe sense of morality, however, in the mouth of the villainness, Mrs. Cheveley. Prior to the exchange between the Chilterns, Mrs. Cheveley ventures a biting critique of Victorian society, decrying its "modern mania for morality." Whereas scandals once lent charm to a politician, they now spell his ruin. Ultimately, of course, for Mrs. Cheveley it takes little more to assuage those of rigid morals than a few insipid homilies. As she remarks: "In modern life nothing produces such an effect as a good platitude. It makes the whole world kin."
More humorously, Lady Basildon and Mrs. Marchmont mock the notion of the ideal husband while bantering with Lord Goring. Bemoaning unendurably ideal husbands as dreadfully dull, they declare themselves "martyrs" of married life. Their conversation thus perhaps ironizes Lady Chiltern's worship of her ideal mate and her imminent martyrdom as a deceived wife.
Finally, we should also note the introduction of two objects on stage: the letter that returns from Sir Robert's past and the diamond bracelet. Such lost, misplaced, and waylaid objects are also familiar devices from the Victorian stage, serving to complicate plot and produce moments of dramatic irony. We will return to these objects in more detail below.