Duke Orsino is in love with Lady Olivia, but she won’t have anything to do with suitors. Viola is shipwrecked and believes her twin brother Sebastian to be dead. She pretends to be a boy and becomes a servant to Orsino and gets sent to woo Olivia. However, Olivia falls in love with Viola, believing her to be a boy. Viola falls in love with Orsino.
Sir Toby Belch (Olivia’s uncle), Sir Andrew Aguecheek (his friend), Maria (a maid), Feste (a jester) and Fabian (a servant) plot to make a fool out of Malvolio (Olivia’s head steward). They write a letter, apparently from Olivia, in which she confesses her love for Malvolio and wishes him to dress and behave in a ridiculous manner. Believing that this will get Olivia to marry him, he does everything the letter asks but Olivia, who knew nothing about this, has him locked away for being insane. They eventually set him free but he is furious. Sebastian, Viola’s brother, turns up and, believing him to be Viola (who Olivia thinks is a boy) she asks him to marry her and he does. Viola’s identity is revealed and Orsino falls in love with her and they marry and it is revealed that Sir Toby and Maria have also married.