The background of the play’s first scene is set in the flat of the wealthy Algernon Moncrieff, who is also known as Algy, in the Mayfair area of West London. He is expecting a visit from his aunt, Lady Bracknell, and her daughter, and Algy’s cousin, Gwendolen Fairfax. He is surprised to find that it is his friend, Mr. Ernest Worthing, who has arrived ahead of them. Ernest notices the elaborate tea service and inquires after the guests for whom Algy is waiting. When he gets to know that Gwendolen will be arriving with her mother, he is delighted and makes it known to his friend that he plans to propose to her. Algy is dismissive and points out that since Gwendolen is his first cousin, Ernest would also have to ask for his permission if he wishes to ask for her hand in marriage. He further submits a proof of his wariness towards Ernest: a cigarette case Ernest had left behind the last time he was at Algy’s. The case is inscribed ‘From little Cecily with her fondest love.’ Algy demands an explanation regarding Ernest’s actual identification.
Ernest reveals that his real name is Jack Worthing and he was adopted as a boy by a gentleman, Mr. Thomas Cardew, who also made him the guardian to his granddaughter, Cecily. Jack lives on a country estate with his ward and her governess, Miss Prism. He refuses to disclose the address of his estate to Algy but explains why he has created an imaginary younger brother called Ernest Worthing whose identity Jack assumes in the city as an escape from his real role as the uncle to an heiress. After listening to Jack’s justification, Algernon too has a confession to make. He occasionally excuses himself out of boring engagements by visiting an imaginary ill friend with the name of Bunbury. While the two friends discuss the implications of their escapades, Lady Bracknell and her daughter arrives.
Lady Bracknell invites Algernon to her reception party but he excuses himself from attending the party with the reason being that he needs to visit his invalid friend, Bunbury, on that day. He takes her into the other room, thus, giving Jack Worthing the opportunity to talk to Gwendolen privately. He is unable to confess his intentions but Gwendolen is able to see through his hesitation and expresses her feelings on the matter herself. She accepts his proposal but reveals that the larger part of her attraction towards him comes from his name, Ernest, which she finds deeply aristocratic. Had his name not have been Ernest, she would never have considered him an appropriate suitor. Jack resolves privately to change his name.
Lady Bracknell enters the room and Gwendolen makes known her intentions of marrying Jack Worthing. Her mother, therefore, proceeds to interview him to evaluate his eligibility as a suitor for Gwendolen. All is going well until Jack reveals that he was adopted as a child and therefore has no real social status by birth. She refuses to give her permission and forbids Gwendolen from seeing Jack Worthing again. Gwendolen, however, is adamant and stealthily acquires the address of Jack’s estate from him, an act that is observed by Algy who writes it down on his shirt cuff.
This is where the second act starts. The location has been replaced by Jack Worthing’s country estate, where Miss Prism, Cecily’s governess is teaching her student the difference between good and evil. She offers the vast difference in character between her uncle, Jack Worthing and his younger brother, Ernest. One is sensible and responsible while the other is wayward and has a loose character. Meanwhile, amongst all these preachings, the local vicar, Canon Chasuble, makes his arrival known and offers to take Miss Prism for a walk. Miss Prism and the vicar leave the scene, leaving Cecily alone in the garden. She is then acquainted with Algy, who introduces himself as Ernest Worthing, Jack’s younger brother. Algy is fascinated by Cecily’s beauty and resolves to get to know her more without any interference on Jack’s part. He spends the whole weekend on Jack’s estate but intends to leave before Jack is due to arrive on Monday. However, his plan is foiled when Jack arrives with an act of his own. He has noticed Cecily’s growing attraction towards his imaginary brother, Ernest, and plans to kill off this imaginary character before things escalate. He encounters Miss Prism and the vicar walking towards the house and informs them of the death of his younger brother in Paris. He further questions the vicar regarding the rechristening of his name, intending to change it to Ernest, to the preference of Gwendolen. He is shocked to find that Algy has reached his estate and is posing as the brother he intended to kill off. He urges Algernon to leave, arranging for his departure but Algy is determined and resolves to stay. When Jack leaves the scene in order to change out of his mourning clothes, Algy uses this chance to propose to Cecily, who readily accepts. She reveals that she has been fascinated with the idea of being engaged to him for quite some time now and a greater part of her fascination comes from his name, Ernest. Algernon is elevated that Cecily returns his affections but disturbed that it is due to the name Ernest. He too resolves to change his name from Algernon to Ernest. He leaves the scene, seeking the advice of the vicar, regarding the rechristening of his name.
To make things even more confusing, Gwendolen arrives at the estate and has an encounter with Cecily. Both women regard each other with caution and each discovers that both are engaged to be married to a Mr. Ernest Worthing. Algernon and Jack arrive to the setting, having made arrangements with the vicar about changing their names to Ernest. Now that the gentlemen have arrived, both ladies reveal to each other that their fiancés are, in fact, named, Jack and Algernon. Gwendolen and Cecily demand to know about the whereabouts of the real Ernest Worthing and Jack is forced to confess that there is no such man with this name. Betrayed and seething with wrath, the two ladies leave the scene, forcing Algy and Jack to confront each other regarding the mess that has been created.
The last act begins with Jack and Algy both confessing their crimes to their fiancés and justifying that they only deceived them to receive their affections. Both are relenting but express their disappointment at not being able to marry a man named Ernest. The gentlemen state that they have made arrangements to be rechristened with the name of Ernest, winning over the hearts of their beloved ones at once.
With the end of one problem comes the beginning of yet another. Lady Bracknell has also arrived, having bribed her daughter’s maid into revealing the location of her existence. She is surprised to find Algernon too and deduces that he has come to the countryside to visit his friend, the ill Bunbury. Algy lies and proclaims that his friend has deceased. He introduces his aunt to Cecily who, like her uncle, is also interviewed regarding her social status. Lady Bracknell is impressed with Cecily’s wealth and is in approval of the marriage. However, Jack sets a condition: Lady Bracknell must consent to his union with her daughter, Gwendolen. She refuses to change her decision and all seems to have been lost. Lady Bracknell appears to be getting ready to leave but starts at the mention of the governess, Miss Prism.
She demands to meet her and is confirmed of her suspicions upon being introduced to her. Miss Prism had been in charge of the son of Lady Bracknell’s sister who she had taken for a walk but had never returned. Miss Prism explains that she had misplaced the baby in her handbag and a book she had been working on, in the carriage. She further confesses that she has no idea what happened to the baby.
At this point, Jack starts interrogating Miss Prism himself about the handbag and where she had left it. He leaves the scene only to quickly return with a handbag, a handbag that the governess identifies as the one she had lost twenty-eight years ago. It is revealed that Jack was the lost baby and therefore, the older brother of Algernon. Now that his social standing has been elevated, Lady Bracknell has no qualms about Gwendolen accepting his proposal.
However, the last dilemma is that the party is still unaware of Jack’s real name. Lady Bracknell claims that Jack was named after his father but is unable to recollect the name of her brother-in-law. Fortunately, Jack arranges for military records which show that his father’s name was Ernest John. He is taken aback by the fact that all those lies he has been telling people are actually true and asks for Gwendolen’s forgiveness. He also adds that he has now realized the true importance of being earnest.