The 12th night is formed by 2 stories that are mixed together.
The main story talks about Viola and her twin Sebastian who had disappointed. Viola went to Illyria, she “transformed” herself (she wore male clothes) and became Cesario in order to work for the duke Orsino. Orsino had fallen in love with Olivia, a countess, but she had never married someone after her brother’s death. Unluckily she felt in love with Viola/Cesario. At last Sebastian returned and got married with Olivia and Viola got married with Orsino.
The second story talks about Maria and Malvolio (Olivia’s steward). She play him a truck, she wrote a letter to make Malvolio ridiculous.
Ih the letter she had written that the countess had fallen in love with him and she made some requests (to wear yellow garter and to have hostile attidute) that make Malvolio ridiculous. Everyone thought that he had become crazy and he went to prison too. This second story in an interlude of the first story. The 12th night is set in Illyria.