Importance of Being Earnest

The play is set in "The Present" (1895 at the time of the premiere).

Act I

Algernon Moncrieff's flat in Half Moon Street

Algernon Moncrieff, a young man about town, is visited by a friend whom he knows by the name of Ernest Worthing. The latter has come from the country to propose to Algernon's cousin, Gwendolen Fairfax. Algernon refuses to consent until Ernest explains why his cigarette case bears the inscription, "From little Cecily, with her fondest love to her dear Uncle Jack". Worthing is forced to admit to living a double life. In the country, he assumes a serious attitude for the benefit of his young ward, the heiress Cecily Cardew, and goes by the name of John or Jack, while pretending that he must worry about a wastrel younger brother in London, named Ernest. Meanwhile, he assumes the identity of the profligate Ernest when in town. Algernon confesses a similar deception: he pretends to have a sickly friend named Bunbury in the country, whom he can "visit" whenever he wishes to avoid an unwelcome social obligation. Jack refuses to tell Algernon the location of his country estate.
Gwendolen and her formidable mother, Lady Bracknell, now call on Algernon, who distracts Lady Bracknell in another room while Jack proposes to Gwendolen. She accepts but says she could not love him if his name were not Ernest. He resolves secretly to be rechristened. Discovering the two in this intimate exchange, Lady Bracknell interviews Jack as a prospective suitor for her daughter. Horrified to learn that he was adopted – having been found as a baby in a handbag deposited at Victoria Station in London – she refuses him and forbids further contact with her daughter. Gwendolen manages to covertly promise to him her undying love. As Jack gives her his address in the country, Algernon surreptitiously notes it on the cuff of his sleeve: Jack's revelation of his pretty young ward has motivated his friend to meet her.

Act II

The Garden of the Manor House, Woolton

Cecily is studying with her governess, Miss Prism, in the (fictitious) village of Woolton, Hertfordshire. Algernon arrives, pretending to be Jack's brother, Ernest Worthing, and soon charms Cecily. Long fascinated by her uncle Jack's hitherto-absent dissolute brother, she is predisposed to fall for Algernon in his role of Ernest. Algernon plans for the rector, Dr Chasuble, to rechristen him "Ernest".
Jack, who has decided to abandon his double life, arrives in black funeral attire and announces to Miss Prism and Dr Chasuble his brother Ernest's death in Paris, from a severe chill. His story is undermined by Cecily, who enters to inform Jack that Ernest arrived earlier. Gwendolen enters, having left the Bracknells' London house without her mother's knowledge. During the temporary absence of the two men she meets Cecily. They get along well at first, but when each learns of the other's engagement to Ernest Worthing, hostility between them grows as they assert their respective claims over Ernest. When Jack and Algernon reappear together, Gwendolen and Cecily realise they have been deceived; they leave the men in the garden and withdraw to the house.

Act III

Morning-room at the Manor House, Woolton
Gwendolen and Cecily forgive the men's trickery. Arriving in pursuit of her daughter, Lady Bracknell is astonished to be told that Algernon and Cecily are engaged. The revelation of Cecily's wealth soon dispels Lady Bracknell's initial doubts over the young lady's suitability, but any engagement is forbidden by her guardian, Jack: he will consent only if Lady Bracknell agrees to his own union with Gwendolen – something she declines to do.
The impasse is resolved by the return of Miss Prism, whom Lady Bracknell recognises as the person who, 28 years earlier as a family nursemaid, had taken a baby boy out in a perambulator from Lord Bracknell's house and never returned. Challenged, Miss Prism explains that she had absent-mindedly put into the perambulator the manuscript of a novel she was writing, and put the baby in a handbag, which she later left at Victoria Station. Jack produces the same handbag, showing that he is the lost baby, the eldest son of Lady Bracknell's late sister, Mrs Moncrieff, and thus Algernon's elder brother. Having acquired such respectable relations, he is acceptable as Gwendolen's suitor.
Gwendolen continues to insist that she can love only a man named Ernest. Lady Bracknell tells Jack that, as the firstborn, he would have been named after his father, General Moncrieff. Jack examines the Army Lists and discovers that his father's name – and hence his own original christening name – was, in fact, Ernest. As the happy couples embrace – Ernest and Gwendolen, Algernon and Cecily, and even Dr Chasuble and Miss Prism – Lady Bracknell complains to her newfound relative: "My nephew, you seem to be displaying signs of triviality". He replies, "On the contrary, Aunt Augusta: I've now realized for the first time in my life the vital Importance of Being Earnest".