Twelfth Night (or) What You Will

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 dead. Masquerading as a young page under the name Cesario, she enters the service of Duke Orsino. 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. 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. -Wikipedia