Twelfth Night begins on the shore of Illyria, where Viola has survived a shipwreck but fears that her twin brother, Sebastian, has drowned. After learning about her new surroundings from the ship’s captain, Viola disguises herself as a young man and sets out to find employment from Duke Orsino.
Orsino has been sending messengers to court the Lady Olivia. He is convinced, from what he hears, that she is his ideal match. After Viola (disguised as ‘Cesario’) arrives at his court, it only takes a few days to become a favorite of Duke Orsino. The Duke imagines that ‘Cesario’s’ youthful face will appeal to Olivia and sends ‘him’ to woo her on his behalf. Viola dutifully takes on the task, even though she has fallen in love with Orsino herself!
Meanwhile in Olivia’s house, Olivia refuses to see any suitors because she has dedicated herself to seven years of mourning for her recently deceased brother. Her uncle Sir Toby Belch thinks that his niece is being foolish and brings his friend Sir Andrew Aguecheek, a foolish knight to woo Olivia. They are reprimanded by the maid, Maria, for drinking late into the night and making merry in a house of mourning. Only the fool, Feste can lift Olivia’s spirits.
They are interrupted by news that a messenger from Orsino is waiting at the gate. ‘Cesario’ enters and is granted private audience with Olivia. It becomes clear, as ‘Cesario’ tries to convince Olivia of Orsino’s worthy love, that Olivia is instead falling for ‘Cesario.’ When Viola leaves, Olivia sends her melancholy steward Malvolio to bring a ring to the youth and say it was left behind.
Malvolio intercepts Viola on her way back to Orsino’s and presents the ‘forgotten’ ring, telling her only to return to tell Olivia of how Orsino takes the news of her rejection. Viola accepts the ring in confusion, but realizes to her dismay that this is a sign that Olivia has fallen in love with ‘Cesario’ instead of Orsino!
Elsewhere in Illyria, Viola’s twin brother, Sebastian, has survived the shipwreck but believes that Viola has perished. He too sets off for Orsino’s court. Sebastian’s friend, the sea captain Antonio, has enemies in Orsino’s court, but pledges to come along to keep him safe.
disapproving Malvolio. After he leaves, Maria concocts an elaborate trick to be played on him. Forging a love letter from Olivia, she will encourage Malvolio to take on a series of ridiculous behaviors — all carefully planned to put him out of Olivia’s favor. Sir Toby, Sir Andrew, and Feste all agree to help with the trick, which leads to Malvolio falling for it entirely and being confined as a madman.
Sir Andrew is discouraged by Olivia’s continued favor toward ‘Cesario,” so Sir Toby convinces Sir Andrew to challenge the youth to a duel. Just as they are about to fight, Antonio happens upon the scene and, believing Viola to be her brother Sebastian, intervenes and is arrested. Later Sir Andrew encounters the real Sebastian on the street and re-issues his challenge, but Sebastian soundly beats him. Olivia arrives and mistakes Sebastian for ‘Cesario,’ asking him to marry her. He is immediately smitten by her beauty and agrees.
The appearance of Sebastian in town sends everyone into confusion. Antonio accuses ‘Cesario’ of not repaying they money he lent to Sebastian. Olivia embraces ‘Cesario’ saying they have been married, much to Viola’s shock. Sir Toby and Sir Andrew accuse ‘Cesario’ of assaulting them in the street. In the midst of all Viola’s denials, Sebastian arrives. The twins recognize each other, Viola is revealed as a woman, and they clear up the confusion.
In the end, Viola marries Orsino, Sebastian and Olivia remain happily wed, and Sir Toby offers to marry Maria to make up for all the trouble he has given her. It is only vengeful Malvolio who does not live happily ever after.