Twins Sebastian and Viola are separated after a shipwreck and believe each other dead. Viola disguises herself as a page boy, Cesario, to work for Duke Orsino and falls in love with him, but he loves Olivia, who falls in love with Cesario. Seeing Sebastian one day, she mistakes him for Cesario and marries him. The confusion is cleared up when Viola and Sebastian meet again, and the Duke marries Viola. The subplot concerns the efforts of Sir Toby and Andrew to humble the presumptuous Malvolio.