The Duke of Illyria, Count Orsino, is desperately in love with the Lady Olivia. Olivia, in mourning for her dead brother, has rejected all his advances.
Identical twins Viola and Sebastian survive a shipwrecked voyage from Messaline. They land apart in Illyria but each mistakenly believes the other drowned.
Viola’s first contact is with Feste, an itinerant observer, who explains to her the crazy local politics. Confused, alone and uncertain, Viola disguises herself as a man while she figures out how to survive in this peculiar land.
Sebastian, saved by the pirate Antonio, disguises himself for much the same reasons.
Viola, calling herself Cesario, gets a job as a servant for Orsino. He sends Cesario (who is really Viola) with love letters to woo Olivia on his behalf.
Unfortunately, Viola has secretly fallen in love with Orsino. Even more unfortunately, Olivia is taken in by Cesario/Viola’s disguise and falls in love with him/her!
In the chaos of this country, the servants run amuck and Olivia’s Uncle, Sir Toby, profits from the chaos. Fed up with Olivia’s supercilious butler, Malvolio, constantly spoiling their fun, Toby and the servants decide to trick him into believing that Olivia loves him with a forged letter.
Malvolio does as the letter suggests, and Olivia thinks he has gone mad, so has him locked up.
Confusion abounds with the mistaken identity of Sebastian and Cesario/Viola. They become embroiled in Toby’s schemes and Olivia starts wooing the wrong twin.
All is revealed when the twins are finally reunited. Olivia discovers the trick that has been played on Malvolio, and he's released from confinement. The love octa-gone wrong is resolved into two couples, Sebastian and Olivia, and Viola and Orsino.