Viola is washed up on the shore of Illyria after losing her twin brother in a shipwreck. She dresses as a boy, calls herself Cesario and goes to work for a rich Duke called Orsino.

Orsino grows to like ‘Cesario’ and sends 'him' to carry messages of love to a rich Countess, Olivia. Olivia isn’t interested in Orsino but falls in love with ‘Cesario’ instead.

Olivia’s uncle, Sir Toby Belch, and his friend Sir Andrew get drunk one night and are told off by Malvolio, Olivia’s steward. They plan to get back at him with the help of the maid Maria.

Maria writes a love letter to Malvolio, pretending it’s from Olivia. The letter asks him to do strange things to prove his love for Olivia. Malvolio finds it and vows to do everything the letter asks.

Viola thought her twin brother Sebastian had drowned in the shipwreck but, unknown to her, he arrives in Illyria with his friend Antonio who rescued him.

Viola visits Olivia’s house dressed as 'Cesario' and Sir Toby Belch sets up a duel between ‘him’ and Sir Andrew. Antonio tries to stop the fight, thinking Viola is Sebastian.

Olivia sees Sebastian and thinks he’s ‘Cesario’. She asks him to marry her and Sebastian is surprised but agrees.

Malvolio starts to behave strangely and does all the things he was asked to in the letter. Sir Toby and Maria use this as an excuse to pretend he has gone mad and lock him in a dark room.

After a lot of confusion about who is who, Sebastian and Viola are both seen in the same place at the same time and are reunited. Everything is resolved and Orsino asks Viola to marry him.

Malvolio is finally released from the dark room. He vows revenge on everyone.