Algernon informs Lane that he will be going Bunburying tomorrow. Gwendolen promises to write Jack daily when he returns to the countryside, and Jack escorts her out. She asks Jack his address in the country, and Algernon slyly writes this down and checks a train timetable. Algernon expresses interest in meeting Cecily, but Jack does not want this to happen, as she is young and pretty. Jack tells Algernon what happened, and promises to 'kill off' his brother Ernest later in the week. She is aghast and says she will not allow her daughter to marry him. After she leaves, Lady Bracknell learns from Jack that he was an orphan, found in a handbag on a train. Lady Bracknell says that only she or her father can engage Gwendolen, and orders her to wait in the carriage. Lady Bracknell comes in, and Gwendolen informs her of their engagement. Jack asks if she would still love him if his name were not Ernest. Jack confesses his feelings to Gwendolen, and she admits that she likes him, too, especially since she has always wanted to love someone named Ernest. Algernon tells Lady Bracknell that he will be unable to attend her dinner tonight, as Bunbury is ill. Jack insists that he is through with 'Ernest,' but Algernon maintains that he will need him more than ever if he marries. Algernon confesses that he has invented an invalid in the country, Bunbury, for when he needs to get out of town.

He has invented a ne'er-do-well younger brother named Ernest who lives in Albany, and whose problems frequently require Jack's attendance.

Since Jack must maintain a high level of morality to set an example, he needs an excuse to get into town. Cecily now lives at Jack's place in the country under the guidance of her governess, Miss Prism. Jack explains that Thomas Cardew, who adopted him, willed Jack to be guardian to his granddaughter, Cecily. Algernon says he has always suspected Jack was a 'Bunburyist,' and now he has proof. Algernon orders Lane to bring in Jack's cigarette case and shows the inscription: ''From little Cecily, with her fondest love to her dear Uncle Jack.'' Jack says his name is Ernest in town and Jack in the country.

Algernon ridicules the notion of marriage, and says that before Jack can marry Gwendolen, he has to clear up the issue of Cecily. Jack reveals he has come to London to propose to Gwendolen. His butler, Lane, brings in 'Ernest Worthing' (who is listed as 'John Worthing' in the cast list and 'Jack' in the body of the play, although both Lane and Algernon believe his name is Ernest), who has just returned from the country. Algernon Moncrieff prepares for the arrival of his aunt, Lady Bracknell, and her daughter, Gwendolen, in his stylish London flat in 1895.

On the importance of being earnest