* Viola, a young woman, disguises herself as a man named Cesario and enters the service of Orsino, the Duke of Illyria.
* Orsino is in love with Olivia, a wealthy countess, but she rejects his advances.
* Olivia, in turn, falls in love with Cesario, unaware that he is actually a woman.
This love triangle leads to a series of misunderstandings and complications that form the central conflict of the play.