Duke Orsino has convinced himself that he is in love with Olivia, who is mourning the recent deaths of her father and brother.
She refuses to see entertainments, be in the company of men, or accept love or marriage proposals from anyone, the Duke included, until seven years have passed.
Viola (who is disguised as a boy in the play) is interested with and falls in love with Duke Orsino, but Duke is in love with Countless Olivia.
Upon meeting Viola, Countess Olivia mistakes her for a man and in turn falls in love with her.
Viola is shipwrecked on the coast of Illyria and she comes ashore with the help of a Captain.
She has lost contact with her twin brother, Sebastian, whom she believes to be drowned, and with the aid of the Captain, she disguises herself as a young man under the name Cesario and enters the service of Duke Orsino.
Upon meeting Viola, Countess Olivia falls in love with her thinking she is a man.
The play expanded on the musical interludes and riotous disorder expected of the occasion, with plot elements drawn from the short story "Of Apollonius and Silla" by Barnabe Rich, based on a story by Matteo Bandello.
The play centres on the twins Viola and Sebastian, who are separated in a shipwreck.
Viola (who is disguised as Cesario) falls in love with Duke Orsino, who in turn is in love with Countess Olivia.