In Illyria, Duke Orsino bemoans his unrequited love for the Countess Olivia. Viola and a Captain wash up on the shore after a shipwreck that Viola believes killed her twin brother, Sebastian. She grieves for Sebastian, but resolves to make a life for herself in Illyria. When the Captain tells her of Orsino she decides to dress as a boy and work as his servant.
At Olivia’s house, Olivia’s drunken cousin, Sir Toby Belch, convinces Sir Andrew Aguecheek to try to win Olivia’s hand in marriage. Viola, disguised as a youth named Cesario, begins to serve Duke Orsino. She becomes Orsino’s favorite, and he sends her to Olivia’s house on his behalf, not knowing Viola has fallen in love with him.
When Olivia reluctantly agrees to see Viola, Viola criticizes Olivia’s refusal to listen to Orsino’s pleas of love. Viola’s harsh words cause Olivia to fall in love with her and Olivia sends her servant, Malvolio, after Viola with a ring. When Malvolio presents the ring to Viola, she realizes that Olivia has fallen in love with her. Meanwhile, Olivia’s brother Sebastian finds himself in Illyria with a sailor, Antonio, who guides Sebastian into Illyria even though he is a wanted man.
Toby, Andrew, Feste (the clown), and Maria (a servant)have grown tired of Malvolio spoiling their parties in Olivia’s house. They decide to play a trick on him, leaving letters that imply Olivia loves him. The letters say that in order for Malvolio to show his love for Olivia he must wear yellow, cross-gartered, stockings and smile at her.
Olivia declares her love for Viola, but Viola refuses her. Sir Andrew sees Viola and realizes that his chances at winning Olivia are slim. Sir Toby and Fabian encourage him to challenge Viola to a duel. Meanwhile, Antonio gives Sebastian some money so that Sebastian can entertain himself in the city. Malvolio follows the advice of the trick letters, appearing before Olivia with yellow stockings and a terrifying grin. Olivia assumes Mavolio has gone mad and orders Sir Toby
to look after him.
Sir Toby meets Viola and presents her with a note from Sir Andrew challenging her to a duel. Neither Andrew nor Viola wish to fight and as soon as they draw their swords, Antonio, mistaking Viola for Sebastian, rushes to save her. Two officers of the Duke arrive and arrest him and when Antonio asks for his money, Viola cannot produce it.
Not long after, Sebastian encounters Sir Toby, Fabian, and Sir Andrew. Believing that he is Cesario they try to attack him, but Olivia arrives and fends them off. Believing that Sebastian is Cesario, she invites him to her house and Sebastian accepts her invitation. Maria and Feste decide to play a trick on Malvolio who has been locked away in a dark room. Feste pretends to be the curate “Sir Topas,” and performs a fake exorcism on Malvolio. Soon after, Olivia proposes to Sebastian and they leave to be married.
Orsino, ignorant of Olivia’s marriage, goes to visit her house with Cesario. Orsino’s officers bring Antonio to him, and Orsino identifies Antonio as his enemy. Olivia enters, and Orsino tries to speak to her, but she says she already married Viola. Both Orsino and Viola are shocked, and Orsino tries to send Viola away. Sir Toby and Sir Andrew enter, both saying they were injured in a fight with Cesario. Sebastian enters, looking identical to Viola. The brother and sister have a joyful reunion and Viola reveals herself as a woman. Orsino proposes to her and she accepts. Malvolio arrives, freed from his dark room, and Maria, Toby, Andrew, and Feste’s plot against him is revealed.