The setting is the garden in the Manor House—Jack’s country estate. It’s July. A table full of books is set up beneath a yew tree in the rose garden. Miss Prism is sitting at the table while Cecily is in the back, watering the flowers.
Miss Prism calls to Cecily to stop doing such a mundane task as watering the flowers because she needs to do her German grammar lesson.
Cecily argues that she doesn’t want to because she knows she looks plain after her German lesson.
Miss Prism retorts that Uncle Jack is only looking out for Cecily’s education.
Cecily complains that Uncle Jack is so serious.
Miss Prism defends him as the pinnacle of "duty and responsibility" (II.5). She adds that he’s even helping out that unfortunately troublesome younger brother of his.
This piques Cecily’s interest and she wishes aloud that Uncle Jack would bring Ernest by sometime so that Miss Prism could reform him.
She begins writing in her diary, where she keeps all the "wonderful secrets of [her] life" (II.10). At this, Miss Prism comments that she was once a writer herself.
She wrote a three-volume novel (the bane of Cecily’s existence) back in the day. Miss Prism tells Cecily to work on her lesson.
But the perfect excuse to ignore the lesson is just arriving—Dr. Chasuble. At the sight of him, Miss Prism blushes and stands.
They’re so obviously crushing on each other that Cecily finds it easy to persuade them to take a walk together.
While they’re out, Merriman the butler tells Cecily that a Mr. Ernest Worthing has just arrived.
Cecily is overjoyed to finally be able to meet the infamous Ernest, but she’s scared at the same time.
Algernon enters, disguised as Ernest. He greets his "cousin," Cici. They talk about how "wicked" he is, with Cecily making comments about how he should reform himself.
Charmingly, Algernon/Ernest asks Cecily to try to reform him that very afternoon.
As they’re flirting and Ernest is finding every way possible to compliment Cecily, like asking for a pink rose for his button-hole "because you are like a pink rose, cousin Cecily" (II.75).
Algernon learns that Jack plans to send Ernest to Australia.
As Cecily’s putting a flower into his buttonhole, Miss Prism and Dr. Chasuble return, discussing the moral advantages and disadvantages of marriage. They’re so wrapped up in each other that they don’t realize that Cecily is not where they left her.
Before they can send out a search party, Jack arrives home, dressed in a black suit of mourning.
When they ask him about it, Jack announces that he’s returned early because his brother Ernest is dead. He died last night in Paris of a "severe chill."
When Dr. Chasuble offers to perform a funeral ceremony for Ernest, Jack suddenly remembers something. He asks Dr. Chasuble if he can be christened. After some questions, Dr. Chasuble relents and they arrange for Jack to come by at half-past five that evening.
Cecily comes from the house to meet her Uncle Jack with the happy news that his brother Ernest arrived just recently and is now in the dining-room.
Jack is completely confused.
Dr. Chasuble—trying to smooth over the awkward situation—says that these are good tidings indeed (that Ernest is alive and all). The mystery is solved when Jack sees Algernon sitting at the table.
Jack refuses to shake hands with Algernon. We learn from Cecily that Ernest has been telling her about his poor friend, Mr. Bunbury.
Finally, Cecily declares she will never speak to Uncle Jack again if he doesn’t shake hands with Ernest. Jack gives in reluctantly and Miss Prism praises Cecily for her wonderful act of kindness today. They leave Jack and Ernest together.
Furiously, Jack tells Algy to leave at once. But he’s interrupted when Merriman comes in to reveal that Mr. Ernest’s luggage has been put in the bedroom next to Jack’s.
Jack tells Merriman that unfortunately Ernest’s dog-cart has arrived to take him away; he’s been called back to town.
While Jack rants at Algernon, Algernon talks about how pretty Cecily is. Jack declares the dog-cart is here and leaves, just in time to miss Algy’s comment that he has fallen in love with Cecily.
Cecily appears with a watering can in her hand. She and Ernest/Algernon exchange glances. She pleads with Merriman to let Ernest stay for another five minutes.
Algernon informs her that Jack is sending him away and compliments her beauty. Flattered, Cecily begins copying his words down in her diary, but refuses to let him look at it.
When the dog-cart comes again, Ernest tells it to come again next week.
Without ceremony, he asks Cecily to marry him. She responds amusedly that they’ve been engaged for months.
She confides her past fantasies to him, as they’re written in her diary. Apparently, Ernest proposed on Valentine’s day but they’d broken it off a month later. Now they’re back together, which she can prove with the many love letters from him that she has saved (and written herself).
Ernest kisses her for being so forgiving.
Then she confides that it’s always been a "girlish dream of mine to love someone whose name was Ernest" (II.233).
Distraught, he asks her if she could love him under any other name… say… Algernon, for instance.
Cecily finds it a rather aristocratic name, but no, she wouldn’t be able to love him then.
At that declaration, Ernest/Algernon promptly begins asking her about the rector and whether or not he performs christenings.
Algernon leaves to find Dr. Chasuble about a very important matter. As he leaves, Cecily comments that she likes his hair so much.
Soon, Merriman enters to tell Cecily that a Miss Fairfax has arrived to see Mr. Worthing.
Cecily invites Miss Fairfax to sit with her until Uncle Jack comes out.
They’re both such charming girls that when they meet, they declare they’ll be best friends and call each other immediately by their first names.
They talk for a little while before Gwendolen works up the balls to ask Cecily if she can inspect her.
Gwendolen, peering through her glasses, finds Cecily rather too attractive and loudly wishes that she were a bit older and more decidedly more dowdy. She asks about Cici’s relations and finds out that Mr. Worthing is Cecily’s guardian.
Now that’s problematic, Gwendolen says, since Ernest never mentioned it to her.
When Cecily hears the name Ernest, she quickly explains the situation.
It’s not Ernest Worthing who is my guardian, she says sweetly, but his older brother, Jack.
That’s a relief to Gwendolen, who suddenly becomes polite again.
Cecily proudly declares that she’s going to be Ernest Worthing’s wife.
Gwendolen rises to her feet. Excuse me? You’re mistaken. Ernest proposed to me yesterday. Cecily retorts that he must’ve changed his mind because he just proposed to her ten minutes ago. The two women eye each other coldly before Gwendolen announces—alluding to Cecily’s rude manners—that they obviously move in different social circles.
Right before they can start clawing at each other, Merriman comes by to arrange their tea things. The girls bite back their acidic words in his presence.
As Merriman serves them, they glare at each other but chitchat in cordial tones. However, their small talk bristles with little insults, mostly about the superiority of urban life (from Gwendolen) vs. the superiority of country life (from Cecily).
When Cecily serves Gwendolen tea, she serves it in the opposite manner that Gwendolen requests—giving her lots of sugar in her tea and cake instead of bread and butter.
Thank goodness, Jack arrives just in time to break up their fight.
When Gwendolen jumps on him and asks if he’s to be married to Cecily, Jack laughs it off and kisses Gwendolen.
The truth comes out. Cecily replies that he’s not Ernest Worthing; that’s Uncle Jack.
At the unglamorous name, Gwendolen recoils in disgust.
Right on cue, Algernon enters and Cecily goes through the same routine with him. When he confirms he’s not to be married to Gwendolen, she allows him to kiss her.
This time it’s Gwendolen's turn to clear up the confusion. She reveals that he’s not Ernest Worthing; it’s Algernon Moncrieff, her cousin.
Cecily backs away when she hears "Algernon."
The two women embrace each other in distress, while the men hang their heads in shame.
They finally ask Jack who Ernest is and he is forced to admit that Ernest doesn’t exist.
When both girls realize with horror that neither of them are engaged to Ernest, they agree to go into the house where the men won’t dare to follow them. With scornful looks, they leave.
Infuriated and frustrated, the two men turn on each other for the horrible results of their Bunburying.
Both blame each other for deceiving the girls. They argue for a while and Algernon sits down agitatedly and begins to eat the muffins left by the ladies.
Jack comments that it’s heartless for him to eat so calmly when they’re in such a state and begins fighting with him over the muffins.
In the midst of their squabbling, each discovers that the other has a christening to attend that evening to be named Ernest. Their christenings are scheduled only fifteen minutes apart!
Both try to dissuade each other from doing so, without success.
The act ends with both guys still munching muffins and bickering with each other.