Sir Andrew is very jealous of Cesario because he holds the attentions of the Countess Olivia, even though Cesario is really Viola in disguise. He challenges Cesario to a duel at the prompting of Sir Toby.
Malvolio, who is also in love with Olivia, begins to act like a crazy person as he follows instructions from a fake letter until he is locked in a dark room. Feste, the Fool, dresses as a priest and taunts him, making Malvolio begin to wonder if he really has gone mad.
A shipwreck at the beginning of the play places twins Viola and Sebastian on the island of Illyria, in the western Balkan islands. Each believes the other has drowned at sea, and they both think they have now lost all of their family members.