Before the play begins, twins Viola and Sebastian are separated on the coast of Illyria after their ship wrecks. Both believe the other to be dead. Orsino, a lord in Illyria, is lovesick over Olivia, who has refused his advances. Olivia’s brother has died and she will see no one. When Viola washes up on shore she decides to disguise herself as a boy, call herself Cesario, and join Orsino’s court. Viola (as Cesario) quickly endears herself to Orsino, who tells her to deliver a message of love to Olivia. Unfortunately for Viola, she has fallen in love with Orsino.
At Olivia’s household, Sir Toby (her Uncle) and Sir Andrew (his friend) keep drinking and carousing, much to Olivia’s chagrin. Maria tries to keep the peace between them. Feste, the fool, returns after an absence and wins his way back into Olivia’s good graces. Malvolio, Olivia’s uptight steward, is not happy about Feste’s return. Soon, Olivia hears that there is a man at her gate who will not leave. Viola (as Cesario) enters and demands an audience with Olivia. Viola speaks highly of Orsino and the two exchange words in a battle of wits. Olivia doesn’t want to see Orsino, but she asks “Cesario” to come back again. Olivia is impressed by “Cesario’s” wit. She tells us she has fallen for “Cesario.”
It’s revealed that Antonio, a sea-captain, rescued Sebastian. Sebastian thanks Antonio but says they must go their separate ways. The two say goodbye, but Antonio gives Sebastian some money and says that they will meet up at the Elephant. Antonio warns Sebastian that he is a wanted man and must keep a low profile. Meanwhile, Malvolio finds “Cesario” and returns a ring from Olivia. Viola knows that she didn’t leave a ring and realizes that Olivia loves her. Viola is shocked and decides that time will sort this whole thing out.
Toby, Andrew, and the Fool get drunk and sing songs. Maria warns them to be quiet, but instead of heeding this warning, they sing louder. Malvolio enters, having been woken up by their drunken song. He chews them out and storms off. Sir Toby, Sir Andrew, and Maria decided they’ve had enough of Malvolio’s attitude. Maria writes a note that looks like Olivia’s handwriting. In the note she says, in a riddle, that Olivia is secretly in love with Malvolio.
Back in Orsino’s camp, Viola (as Cesario) and Orsino listen to sad music and bond. They talk about women and how painful it is to be in love. Orsino is talking about Olivia and Viola is secretly talking about her love for Orsino. Fabian has joined Sir Andrew and Sir Toby and they wait for Malvolio to find Maria’s note. They don’t have to wait long. Malvolio finds the note and buys it, hook, line, and sinker. Malvolio confesses his secret love for Olivia and runs off to change into his yellow stockings like the letter asked him to.
Olivia finds Viola and tells her that she is in love with “Cesario.” Viola tells her that they cannot be together, and that Olivia should love Orsino instead. Sir Andrew tells Sir Toby that he wants to leave. Andrew has been trying to woo Olivia and it hasn’t worked. Andrew is mad because Olivia is paying more attention to Cesario than to him. Toby convinces Andrew to write a challenge to Cesario.
Maria is tending to Olivia when Malvolio returns. Malvolio is following the instructions of the letter, so he is dressed in yellow stockings, smiling like a maniac, and kissing his hand. Olivia thinks Malvolio has gone crazy. Toby, Fabian, and Maria act like Malvolio is crazy and decideto lock him up in a dark room. Toby and Fabian run into Viola. Toby delivers Andrew’s letter to “Cesario” and convinces him that Andrew is a fierce warrior. Fabian grabs Andrew and convinces him that “Cesario” is a fierce warrior. Andrew and “Cesario” are terrified to fight one other. Antonio breaks up the action, believing that “Cesario” is Sebastian and that he is under attack. This causes the guards to arrest Antonio, who asks for the money he leant Sebastian. Viola has no idea what Antonio is talking about and Antonio is taken away.
Feste mistakes Sebastian for Cesario and tells him that Olivia wants to see him. Sebastian is understandably confused. Toby shows up with Andrew who he has riled up again. Andrew confronts Sebastian thinking he’s Cesario. Sebastian quickly puts Andrew in his place. Toby jumps in to help Andrew and that’s when Olivia shows up. She gives Toby a tongue lashing and tells Sebastian, thinking he’s Cesario, to come along. Sebastian is immediately smitten and does as he is told.
Feste puts on a disguise, calling himself Sir Topas, and goes to Malvolio to torment him. Malvolio begs him for help, and after making fun of him a bit, Feste says he will help…eventually. Meanwhile Sebastian marvels at his good fortune. There is a beautiful, rich, woman who likes him for no sensible reason. Olivia shows up and suggests the two of them should get married. Sebastian agrees.
In the final scene of the play all the cases of mistaken identity are brought to a head. Olivia seeks out “Cesario” and finds Viola with Orsino. When Olivia calls “Cesario” husband, Orsino is enraged. Sebastian enters, and everyone is amazed there are two “Cesarios.” Sebastian and Viola are reunited. Viola confesses her feelings for Orsino, Sebastian and Olivia reunite, and Toby and Maria are married. Everyone is happy, except for Malvolio who swears vengeance and storms off.