Jack greets Algernon coldly, furious that Algernon has showed up at his country estate, masquerading as “Ernest” and shocked that he has been talking to Cecily about “Bunbury.” At Cecily’s prompting, Jack begrudgingly shakes Algernon’s hand. Miss Prism, Dr. Chasuble and Cecily leave the brothers alone to talk things out.
Jack and Algernon must pretend to reconcile and switch identities in order to preserve their alter egos. Though Jack resists this transition, the relative ease with which Algernon becomes “Ernest” marks the fluid nature of name and identity in the play.
Outraged, Jack tells Algernon that he has to leave. Algernon insists that that he is staying for week, but Jack asserts that “Ernest” has been called back to town and instructs Merriman to order a dog-cart to take “his brother” back to the train station. Algernon refuses to leave until Jack changes out of his mourning clothes, saying that he is absurdly over-dressed.
Jack goes to change and Cecily comes out to the garden. Before departing, Algernon declares his love for her. But Cecily insists that they have already been engaged for three months. Taking out her diary, she relates their elaborate romance, complete with a ring, a broken engagement, and love letters.
While diaries tend to record fact, Cecily’s diary is an instrument of fiction making. Her diary shows Cecily’s powerful ability to align fact with fiction, as she and Algernon fall in love through her made-up love story between her and the fictional "Ernest" (who she thinks is real).
With their engagement confirmed, Cecily confesses that she has always dreamed of marrying a man named “Ernest” because it inspires “absolute confidence.” When Algernon asks if she could love a man with his own name, she immediately declares her dislike for it. This revelation unsettles Algernon, who rushes to see Dr. Chasuble about getting christened.
Even though Cecily is initially attracted to “Ernest” for his wicked nature, her declaration of love mirrors Gwendolen’s. Like Gwendolen, Cecily holds up “Ernest” as an ideal. Her echo of “confidence” redoubles the irony underscoring her and Gwendolen’s love affairs, because Algernon and Jack are not trustworthy insofar as they are not Ernest. Though it is worth noting that their love is real; their love is in earnest.
Meanwhile, Merriman announces Gwendolen’s unexpected arrival at the manor house to Cecily. The two women, unaware of each other’s connections to Jack or Algernon, greet each other in the garden. Gwendolen assumes that Cecily is a visitor to the house, but shows concern when she learns that Cecily is actually Mr. Ernest Worthing’s young and beautiful ward. Cecily corrects her, informing Gwendolen that Jack Worthing is her guardian. “Ernest” is actually Jack’s brother and her fiancé. Shocked, Gwendolen asserts that she is in fact, “Ernest’s” fiancée, reading an entry from her diary as proof.
Jack and Algernon’s carefully crafted cover stories and fake identities unravel, as Cecily and Gwendolen believe themselves to be engaged to the same man. Mistaken identities motivate their emerging jealousies. Lastly, because diaries read more like fictions in the play, Gwendolen’s diary does not appear as an authoritative source, but a paltry piece of evidence.
Believing that they are both engaged to “Ernest,” Cecily and Gwendolen’s jealousies play out over the course of a tea service. Gwendolen refuses Cecily’s offer of sugar and cake, while making snide remarks about Cecily’s tasteless country upbringing. Cecily responds, dumping healthy doses of both into Gwendolen’s cup and onto her plate, while making comments about the city’s “vulgar” nature.
As tensions come to a head, Jack and Algernon arrive, one after the other, having separately made appointments with Dr. Chasuble to be christened later that day. Gwendolen confronts Jack, asking if he is engaged to Cecily. He firmly denies this. Yet Cecily takes great pleasure in pointing out that Gwendolen’s betrothed is not “Ernest,” but her guardian Uncle Jack. Cecily goes to Algernon’s side and declares that he is “Ernest.” Gwendolen takes even greater pleasure in pointing out that Cecily’s fiancé is not “Ernest,” but her cousin Algernon.
Gwendolen and Cecily each play a part in dismantling the fantasy of “Ernest.” By revealing Jack and Algernon’s true identities to each other they essentially destroy the figure with which they are so enamored. While it is gratifying for Cecily and Gwendolen to expose Jack and Algernon, their mean-spirited revelations showcase an empty truth, where no “Ernest,” or earnest man exists at all.
Realizing that they have both been fooled, Gwendolen and Cecily embrace each other and demand to know the whereabouts of Jack’s brother and their fiancé, “Ernest.” Jack confesses that he does not have a brother at all. Cecily and Gwendolen, distraught at no longer being engaged to “Ernest,” retreat into the house.
Cecily and Gwendolen’s distress at no longer being engaged to “Ernest” shows that they have confused the name they adore with the men whom they admire. They loved the name, not the men. In this way Wilde mocks the Victorian aspect of marriage as a uniting of "names"—wealth and reputation being more important than a possible lover's actual traits.
Realizing that they have ruined their chances of getting married, Algernon and Jack argue about their failed “Bunburying” schemes, which prohibit them from further excursions in town or country. They also debate about who will ultimately take the name of “Ernest” at their upcoming christenings with Dr. Chasuble. Jack asserts that he should take the name because there is no proof that he has ever been christened. Attempting to manipulate his friend, so that he can take the name for himself, Algernon insists that such a name change could be dangerous. Meanwhile, the two men squabble over muffins and teacake, until the curtain drops.
Jack and Algernon do not bemoan the loss of their fiancées, but the loss of a good alibi for Bunburying—“Ernest.” Without “Ernest” their double lives in the country and city can no longer live on. Even as the fictional “Ernest” disappears, Jack and Algernon still fight over who will actually assume his name in real life, showing their willingness to make real this character to please their partners. Their quarrel over muffins parallels Cecily and Gwendolen’s fight under the pretense of a civil tea service.