In the main plot of this play, 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. Meanwhile Sebastian, Viola's brother, believed deceased, arrives on the scene, sowing confusion. Mistaking him for Viola, Olivia asks him to marry her, and they are secretly united. Finally, when the twins appear in the presence of both Olivia and the Duke, there is more wonder and awe at their similarity, at which point Viola reveals she is really a female and that Sebastian is her lost twin brother. The play ends in a declaration of marriage between the Duke and Viola, and it is learned that Toby has married Maria.In the subplot, several of Olivia's household conspire to make Malvolio, Olivia's pompous head stewart, believe that Olivia wishes to marry him. She takes his subsequent actions for madness and leaves him to the mercies of his tormentors. At the end of the play Malvolio learns of their conspiracy and storms off promising revenge. (Summary from Wikipedia/Karen Savage)