Gwendolen and Cecily are watching Jack and Algernon through the window. They believe the men look repentant. When they see the men coming back to the house, they decide they will not be the ones to speak first. However, they both break this vow. Cecily asks Algernon why he pretended to be Ernest, Jack’s brother. He replies that he wanted to meet her. Cecily doesn’t quite believe him but is pleased by his answer nonetheless. Gwendolen asks if Jack pretended to have a brother so he had an excuse to come to town and see her. Jack agrees this is the case. The women decide that the men are being honest and should be forgiven. However, both women hate both men’s names. Jack and Algernon tell them that they are willing to be rechristened and had made plans to do so this afternoon.
Merriman announces Lady Bracknell. She learned of Gwendolen’s whereabouts from her maid. She insists that Jack cease seeing Gwendolen. He refuses, saying they are engaged to be married. She refuses to acknowledge the engagement.
She asks Algernon if this is Bunbury’s residence. He says no and reveals that Bunbury died suddenly. Lady Bracknell is glad that he finally made up his mind.
She then asks Jack who is holding Algernon’s hand. Jack introduces his ward Cecily, whom Algernon announces he plans to marry to marry her. Lady Bracknell asks about Cecily’s family background. Jack gives the information and claims he has the documents to prove it. He also refers her to Cecily’s solicitors, who are well-known as the highest in their profession. Lady Bracknell is about to leave until she hears about Cecily’s fortune, which is 130,000 pounds. She suddenly notices how pretty Cecily is and her potential as a society woman. She gives her consent for the marriage.
Lady Bracknell wishes for Algernon and Cecily to be married as soon as possible before they can find out each other’s characters. Jack refuses to give his consent, much to the consternation of Cecily and Algernon. He considers Algernon to be immoral, and Cecily isn’t of age. She won’t be of age until she is 35 years old. Algernon and Lady Bracknell are willing to wait, but Cecily claims she is too impatient. Jack offers his consent if Lady Bracknell offers her consent for him to marry Gwendolen. She refuses.
Dr. Chasuble enters to do the christenings. Lady Bracknell doesn’t approve of Algernon doing this. Jack tells Chasuble that there is no point in doing them now. Dr. Chasuble then says he’ll return to the church where Miss Prism is waiting for him. Lady Bracknell recognizes the name and asks if the woman is a teacher. Her manner of asking offends Chasuble. Jack says that Miss Prism is Cecily’s governess.
Lady Bracknell wishes to see her. Miss Prism enters at this moment, chiding Dr. Chasuble on not meeting her when he said he would. When she sees Lady Bracknell, she pales. Lady Bracknell demands the location of the baby. She tells the astounded company that 28 years ago, Miss Prism left Lord Bracknell’s house with a male infant. His stroller was found with her manuscript inside, but he remained missing.
Miss Prism admits that she has been haunted by this for years. In a distracted state of mind, she accidentally put the manuscript in baby carriage and the baby inside her purse. She left the handbag at the train station, and she has no idea what happened to the baby.
Jack leaves the room quickly and returns with the handbag he was found in. Miss Prism identifies it as her purse. Jack goes to embrace her, thinking she is his mother. Lady Bracknell corrects him, saying he is actually the son of her sister—and Algernon’s older brother.
Lady Bracknell tells Jack he was christened and given his father’s name. She doesn’t remember it. Jack looks it up in the Army Lists and discovers it was Ernest. As it turns out, his lies were actually true.
Everyone lives happily ever after. Jack can marry Gwendolen. Algernon can marry Cecily. Dr. Chasuble can marry Miss Prism.