Archer is stunned at Mrs Mingott's news. He feels that Ellen, frightened at the prospect of his making a decisive step from which there would be no possibility of return, has decided to compromise and have an affair with him. He worries that an affair might draw them into a life of lies and deceptions, and is concerned about how he will be perceived by society.
He waits near Beaufort's house for Ellen. When she comes out, he grasps her hand and tells her that they will be together. He notices Lefferts and Chivers discreetly avoiding them, and is sickened by the thought that this could be their future. They arrange to meet the next day at the Metropolitan Museum.
In the museum, Ellen tells Archer that she has decided to stay with Mrs Mingott because she feels she will be safer from temptation. She does not want to do irreparable harm, as others do in such situations. Archer protests that he is no different from the others; he has the same longings. She wavers, and asks if she should come once to him and then leave New York and go back to her husband. Archer does not believe they can give up their current lives. He miserably agrees that she will come to him the day after tomorrow.
At home, May tells Archer that she has seen Ellen and had a long talk with her. She has decided that she has judged her too harshly and that she is fond of her despite her tendency to take up odd people. But she remarks that she has alienated the van der Luydens by going to visit the disgraced Regina Beaufort.
The following evening, at the van der Luydens' pre-opera dinner, the topic of discussion is the Beauforts' ruin. Mrs van der Luyden asks May if it is true that Mrs Manson Mingott's carriage was outside Mrs Beaufort's door, an action they consider improper, given the Beauforts' disgrace.
Archer and May go to the opera. May is dressed in her wedding dress, a common custom during the first year or so of marriage. Moved by the memory of her generosity when she told him she did not want her happiness to be made out of another's misery, he feels inspired to tell her the truth about Ellen, and ask for his freedom.
At home, he begins to confess about himself and Ellen, but May stops him, saying that none of this matters now that "it's all over": Ellen is returning to Europe to live with Medora.
Archer laughs bitterly, and goes to bed.
May tells Archer that she wants to hold their first big dinner party, in honor of Ellen, who is leaving for Europe. Ellen is not, however, returning to her husband, and Archer thinks there is nothing to prevent him following her. His confidence in their future together has enabled him to restrain himself from contacting her. Mrs Mingott has given Ellen a generous trust fund.
Ellen arrives at the Archers' dinner party, looking pale and almost ugly, though Archer thinks that he has never loved her more than at that moment. The guests are all kind to Ellen, now that she is leaving and will no longer pose a threat to their conventions. Suddenly, he realizes that everyone there thinks that he and Ellen are lovers. He now sees the dinner guests as conspirators in an elaborate ritual to mark the expulsion from the tribe of a member who has transgressed its code. He catches May's triumphant eyes; in the secret war between her and Ellen over Archer, she is the victor.
As Archer bids Ellen goodbye, he says he will see her in Paris. She replies pointedly that he and May will be welcome. Lefferts catches him by the sleeve, asking him to cover for an illicit rendezvous.
After their guests have left, Archer tries to tell May once more of his feelings for Ellen. He begins by saying that he wants to go away on a long trip. May says that he must take her with him, because she is pregnant. She is now sure, though she suspected it two weeks ago, and pretended to Ellen even then that she was sure.
Faced with the prospect of an affair with Ellen, Archer is concerned about how this would appear to society. Contrary to his earlier belief that men who have illicit love affairs are seen as foolish, whereas women who do so are seen as criminal, he is now convinced that the men are judged more harshly than the women. Archer's fears about how such things are perceived are confirmed by the dinner party scene in Chapter 33. The guests assume, wrongly, that Archer has been unfaithful to May, and rally around her.
Ellen's observation about the exhibits from dead cultures in the museum - that eventually, everything that seems important ceases to matter and ends up with a label saying, "Use unknown" - has immense resonance. The customs and traditions of New York society that circumscribe Archer's and Ellen's lives will one day be forgotten and irrelevant. Though The Age of Innocence is set in the 1870s, Wharton wrote it after World War I and published it in 1920, when the society portrayed in it was already defunct. It is the more tragic, then, that Archer's and Ellen's heartfelt desires are sacrificed to mores that have no more permanent value than obscure items in a glass case.
The scene at the opera echoes the opening scene of the novel. On the face of it, little has changed. But there are important and revealing differences. Then, he was impatient to bring forward the announcement of his engagement to May; now, he is equally eager to dissolve their union. Then, his aim was to protect the honor of the family of his wife-to-be; now, he has less respect for convention and wants to pursue his illicit relationship with Ellen. May's tearing and soiling her wedding dress as she gets out of the carriage after the opera is symbolic of their decayed marriage.
He is on the verge of confessing to May his love for Ellen when she tells him that Ellen is leaving for Europe. Once again, Archer is prevented from pursuing his love for Ellen, and responds with bitter laughter. (The first time was in Chapter 18.) However, these events are not the workings of a cruel fate. Both events have been prompted by Archer's own actions: the first time, by his persistent requests to May's family to bring forward his marriage; and the second, by his reckless decision to push his affair with Ellen into action, and also by his pursuance of family life with May to the point of starting a family. It is later revealed that May too has played a calculating part in Ellen's decision, challenging her husband's view of her as passive and unaware.
The Archers' dinner party in honor of Ellen's departure is perhaps the most bitterly ironic scene in the novel. At last, New York society is behaving generously towards Ellen - but Archer realizes it is only because they are celebrating the expulsion from the tribe of a person who has transgressed their code. He also realizes the reason why it is essential, from their point of view, that she goes: they believe that Archer and Ellen are lovers. The deepest irony lies in the fact that this is the one thing that they have been unable to be. We are left to wonder whether, had they given in to temptation, they would have been any worse off. Has their sacrifice been for nothing?
Archer feels "like a prisoner in the center of an armed camp" (Chapter 33, p. 286), reinforcing the sense that Wharton creates of a war between the individual and society. Prompted by this feeling of imprisonment, Archer announces loudly that he intends to travel soon. Later, he catches May's triumphant eyes and knows that she is the victor in an unspoken war with Ellen, with Archer as the prize.
After the dinner party, Archer makes one more effort to tell May of his feelings for Ellen and break free. He is foiled once again, by her revelation that she is pregnant. Though she was not sure two weeks before, when she had her long talk with Ellen, she told Ellen that she was. This, Archer now knows, was what prompted Ellen not to follow through on the affair with Archer and to go instead to Europe. Faced with a pregnant wife, a mistress has no rights. As May tells Archer her news, her eyes are wet with victory - again, a war metaphor. May, far from the dull-minded innocent that Archer has believed her to be, has revealed herself to be a calculating opponent who glories in her triumph over her rival, Ellen.