One of Shakespeare's Classic Romantic Comedies 

Orsino is in love with Olivia and sends Viola, whom he believes is Cesario, to woo Olivia with love letters; but fate isn't having any of it. Instead Olivia falls for Cesario, and Viola discovers she has feelings for Orsino. It's a brilliant Shakespearean love triangle that is further complicated by a subplot that sees Sebastian rescued from the shipwreck by Antonio, a gentleman and former foe of Orsino; and Olivia's uncle, Sir Toby Belch, plot to make a yellow-stockinged fool out of Olivia's self-important steward, Malvolio, with his partners in crime, Sir Andrew Aguecheek, Maria (Olivia's maid), and Feste the clown. 

What ensues is a hilarious run of misunderstandings, mistaken identities and pranks where Olivia mistakes Sebastian for 'Cesario' and asks him to marry her, 'Cesario' accused of assault, the reuniting of the twins and happy beginnings for Orsino and Viola, Sir Toby and Maria.