Twelfth Night or What You Will is a comedy written by William Shakespeare circa 1601. The events of the comedy take place in the imaginary country of Illyria.
The Duke of Illyria, Orsino is in love with young Countess Olivia, but she still mourns the death of her brother. She decides to lock herself in her house for seven years and ignores all the Duke’s advances. Meanwhile, the terrible storm starts near the coast of Illyria causing a shipwreck. A young noblewoman called Viola survives, but she is the only one on the shore. She decides that her twin brother, Sebastian, has drowned with the rest of the crew and tries to find the work she is suitable for in Illyria. She is told by one of the sailors that she can try herself as a servant of Countess Olivia, but it appears that Olivia doesn’t want to talk to any strangers because of her mourning. Viola then decides to disguise as a man named Cesario and ask Duke Orsino for work instead. Orsino accepts her service.
Viola, as Cesario, quickly earns Orsino’s trust and becomes his page. But Viola finds herself falling in love with her master. Duke, still considering her a man, is oblivious to her feelings and soon sends Cesario to deliver Orsino’s love messages to Olivia. Viola isn’t happy to do this, but obeys. To her joy Olivia rejects Orsino again, falling in love with his beautiful messenger instead. Orsino is desperate. Cesario tries to comfort him, saying that there is another woman who loves him as much as Duke loves Olivia (Viola talks about herself) but Duke angrily rejects “his” words as ridiculous, saying no woman heart can hold such a love. Viola herself is devastated seeing all the troubles her disguise brought to her, the Duke and the Countess. She calls herself “a monster”, but has no other choice than to continue her service as Cesario. This love triangle where everyone loves another person and no love is mutual brings real misery to all three its members.
Leaving them to their feelings, we meet other members of Olivia’s court: Sir Toby, a heavy drinker and Olivia’s uncle and his silly friend Sir Andrew, who believes that Olivia is secretly in love with him. Also we meet Olivia’s witty servant Maria, Festo, the clown of the house, who is the most clever of the whole company and prudish Olivia’s stewart, Malvolio who wants to become a nobleman himself.
Sir Toby, Sir Andrew, Maria and Festo are having a party, but it is disrupted by Malvolio. Malvolio is irritated by Festo’s jokes and tries to convince Olivia to get rid of him. The Countess refuses, because she also considers Festo funny. Sir Toby and Sir Andrew are furious at Malvolio, because he always spoils all the fun, but this time it was too much and Maria decides to pull a cruel joke, using Malvolio’s lack of sense of humor. She writes a fake letter from Olivia, where she confesses love to mysterious M.O.A.I. demanding him, if he loves her too, to wear yellow stockings, smile constantly, do other silly things and never explain himself to anyone. Malvolio discovers the letter, decides that it was written for him and obeys all the demands (yellow stockings, hated by Olivia, included), dreaming about marriage and his new noble status. He appears so weird that Olivia, who doesn’t know anything about the joke, thinks he is mad.
Meanwhile we return to Viola’s brother, Sebastian, who survived the shipwreck with the help of his newfound friend and protector, Antonio, the ship captain. Sebastian, as his sister before, wants to go to Orsino’s land. Antonio has old scores with Duke Orsino and he knows that he will be in danger there, but he is so devoted to Sebastian that he decides to follow the young man anywhere, even when Sebastian declines his help.
Olivia finally talks to Cesario, confessing her feelings, but confused Viola answers that “he” is too young for such a proposal and not interested neither in Olivia nor in any other women. Sir Andrew, who sees Olivia’s obsession with Cesario and hopes to win her appreciation himself, challenges “him” to a duel, mocking Cesario’s shyness when “he” declines the duel. While Sebastian enters the scene, Andrew, cheered by Tony, advances to him and slaps him, thinking he is Cesario. But this time “Cesario” isn’t so shy anymore. The fight is interrupted by Olivia, who suddenly appears and asks Sebastian to marry her, also thinking he is Cesario and hoping that he won’t decline her again. Sebastian is confused, because he never seen the Countess before, but she is young, wealthy and beautiful, so he quickly accepts her proposal. Olivia brings the priest and he quickly conducts the ceremony.
At that time Antonio is captured by Orsino’s guards. He sees “Sebastian” – Viola disguised as Cesario – and asks “him” for help. Viola denies knowing Antonio and the guards drag him off. Antonio cries that Sebastian has betrayed him. Upon hearing this Viola understands that her brother might be alive and decides to search for him.
Malvolio’s “madness” allows Maria and others to lock him in the dark room and continue mocking him. Feste, wearing a priest’s clothes, pretends to examine Malvolio and declares he is insane, disregarding all Malvolio’s desperate pleas. They hold a fake exorcism, torturing Malvolio even more. However, Sir Toby thinks that the joke has gone too far and he allows Malvolio to write a letter to his mistress and ask to be released.
Eventually Viola manages to arrange a visit to Olivia for “his” master. Orsino and Cesario arrive to Olivia’s household, where the Countess greets Cesario as her husband, complaining that he is neglecting her and accusing him of being a bad husband. The Duke is furious, thinking that Cesario betrayed him, secretly marrying the Countess. Then Sebastian appears on stage and everything is finally revealed. Everyone is fascinated by physical similarity of Sebastian and “Cesario” who now openly says that she is Viola. Sebastian apologizes for beating down Sir Andrew and Sir Toby, but says they deserved it and he would gladly do it again if he had the opportunity. The siblings are happily reunited at last. Orsino finally understands why Cesario talked about other woman who is in love with him and accepts the loss of the Countess, deciding to marry Viola instead as soon as she changes off her page clothes.
Malvolio finally appears and yells at Olivia, complaining that she wrote a letter, orchestrating the whole joke by herself. Olivia declines this accusation and then Maria and others have no options that to tell the whole truth about their joke. Malvolio swears to have his revenge to all the people involved and storms off the stage. It becomes known that Sir Toby secretly married Maria in appreciation for her witty scheme of humiliating Malvolio. Now they are also happy together.
Everyone goes to Olivia’s house to prepare for a big party. Festo stays onstage to sing the final song to the audience.