Twelfth Night is a Shakespearean comedy that follows a young woman named Viola, who becomes separated from her twin brother during a shipwreck off the coast of Illyria. Believing her brother to be dead, Viola disguises herself as a man named Cesario and enters into the service of Duke Orsino, the ruler of Illyria. Viola/Cesario quickly becomes Orsino's favorite servant and he sends "him" to woo the Countess Olivia on his behalf. However, Olivia becomes enamored with Viola/Cesario, unknowingly falling in love with a woman she believes to be a man.
Meanwhile, Viola/Cesario also develops feelings for Orsino, which complicates matters as "he" tries to navigate the love triangle. In addition to this, Olivia's pompous and self-important steward, Malvolio, becomes convinced that Olivia loves him, and his delusions are exploited by her drunken uncle and his friends.
As the story progresses, Viola's twin brother Sebastian, who is also in Illyria, is mistaken for her (due to their physical resemblance) and is pursued by Olivia. This leads to a series of misunderstandings and comedic hijinks culminating in a chaotic final scene where all the characters come together.
Overall, Twelfth Night is a witty and clever play that explores themes of love, gender roles, and the nature of identity.