Like many of Shakespeare's comedies, this one centres on mistaken identity. The leading character, Viola, is shipwrecked on the shores of Illyria during the opening scenes. She loses contact with her twin brother, Sebastian, whom she believes is dead. Masquerading as a young page under the name Cesario, she enters the service of Duke Orsino through the help of the sea captain who rescues her. Orsino is in love with the bereaved Lady Olivia, whose father and brother have recently died, and who will have nothing to do with any suitors, the Duke included. Orsino decides to use "Cesario" as an intermediary to tell Olivia about his love for her. Olivia, believing Viola to be a man, falls in love with this handsome and eloquent messenger. Viola, in turn, has fallen in love with the Duke, who also believes Viola is a man, and who regards her as his confidant. Much of the play is taken up with the comic subplot, in which several characters conspire to make Olivia's pompous head steward, Malvolio, believe that his lady Olivia wishes to marry him. (Wiki)