The comedy takes place in a country fabulous for the British Shakespearean time - Illyria.

The duke of Illyria Orsino is in love with the young Countess Olivia, but she is in mourning after her brother’s death and does not even accept the duke’s envoys. Olivia’s indifference only incites the duke’s passion. Orsino takes on the service of a young man named Cesario, whose beauty, devotion and subtlety of feelings he manages to appreciate in just a few days. He sends him to Olivia to tell about his love. In reality, Cesario is a girl named Viola. She sailed on a ship with her beloved twin brother Sebastian and after a shipwreck accidentally ended up in Illyria. Viola hopes her brother also escaped. The girl dresses up in men's clothes and enters the service of the duke, in whom she immediately falls in love. Behind the duke she says: “It’s not easy for you to get a wife; / After all, I myself wanted to be her! ”

Olivia's prolonged mourning does not like her uncle at all - Sir Toby Belch, the merry fellow and the reveler. Cameraman Olivia Maria tells Sir Toby that her mistress is very unhappy with her uncle's drinking and drinking, as well as his drinking companion, Sir Andrew Aiguychik, a rich and stupid knight whom Sir Toby fools, promising to give him his niece, and meanwhile using his shamelessly. Sir Andrew, offended by Olivia’s neglect, wants to leave, but Sir Toby, a flatterer and joker, persuades him to stay for another month.

When Viola appears at the Countess’s house, she is very difficult to let through to Olivia. Despite eloquence and wit, she fails to achieve the success of her mission - Olivia pays tribute to the duke’s merits (he is “undoubtedly young, noble, / rich, loved by the people, generous, learned”), but does not love him. But the young messenger achieves a completely unexpected result for herself - the countess is fascinated by him and comes up with a trick to make him accept a ring from her.

Viola's brother Sebastian appears in Illyria, accompanied by Captain Antonio, who saved his life. Sebastian is grieving about his sister, who, in his opinion, died. He wants to seek happiness at the duke's court. It is painful for the captain to part with a noble young man to whom he has sincerely become attached, but there is nothing to do - it is dangerous for him to appear in Illyria. Yet he secretly follows Sebastian to protect him in case of need.

At Olivia’s house, Sir Toby and Sir Andrew, in the company of the Jester Feste, drink wine and bawl songs. Mary is trying to amiably tempt them. Following her, Olivia’s butler appears - Malvolio’s swaggering bore. He unsuccessfully tries to stop the revel. When the butler leaves, Mary makes fun of this “puffed donkey,” who “bursts with complacency,” and vows to fool him. She is going to write him a love message on behalf of Olivia and put on everyone's laughing stock.

In the duke's palace, the jester Feste first sings him a sad song about unrequited love, and then tries to cheer him up with jokes. Orsino revels in his love for Olivia, previous failures do not discourage him. He convinces Viola to go again to the countess. The Duke makes fun of the alleged youth’s claim that a woman can be in love with him as much as he does in Olivia: “A woman’s chest will not bear the beating / Such a powerful passion as mine.” He remains deaf to all the hints of Viola in love.

Sir Toby and his accomplices are simply bursting with laughter and anger when they overhear, as Malvolio discusses the possibility of marriage with his mistress, how he will tame Sir Toby, becoming the master of the house.However, the most fun begins when the butler finds a letter written by Mary, who forged Olivia's handwriting. Malvolio quickly convinces himself that he is that “nameless lover” to whom it is addressed. He decides to strictly follow the instructions given in the letter and invented by Maria specifically in the hope that the enemy of a cheerful company behaves and looks in the most stupid way. Sir Toby is delighted with the fiction of Mary, and of herself: "For such a witty devil even in Tartarus itself."

In the garden of Olivia Viola and Feste exchange witticisms. “He plays a fool well. / A fool cannot overcome such a role, ”Viola says of the jester. Then Viola speaks with Olivia, who has gone out into the garden, who no longer hides her passion for “young men”. Sir Andrew is offended by the fact that in his presence the countess was courteous with the ducal servant, and Sir Toby convinces him to challenge the impudent youth. True, Sir Toby is sure that both will not have the courage to fight.

Antonio meets Sebastian on a city street and explains to him that he cannot openly accompany him, as he participated in a naval battle with the galleys of the duke and won - “they will recognize me / And, believe me, they won’t let me down.” Sebastian wants to wander around the city. He settles with the captain about meeting in an hour in the best hotel. In parting, Antonio persuades a friend to take his wallet in case of unexpected expenses.

Malvolio, smiling stupidly and tastelessly dressed (all according to Mary's plan), playfully quotes passages from supposedly her message to Olivia. Olivia is convinced that the butler is crazy. She instructs Sir Toby to take care of him, which he does, only in his own way: he first taunts the unfortunate arrogant man, and then stuffs him into a closet. Then mistaken for Sir Andrew and Cesario. He slowly says to everyone that his opponent is fierce and skilled in fencing, but it is impossible to avoid a duel. Finally, the duelists, pale with fear, lay bare their swords - and Antonio, passing by, intervenes. He covers himself with Viola, mistaking her for Sebastian, and begins to fight with Sir Toby, furious that his trick failed. Bailiffs appear. They arrest Antonio on the orders of the duke. He is forced to obey, but asks Viola to return the wallet - he will now need the money. He is outraged that the person for whom he has done so much does not recognize him and does not want to talk about any money, although he thanks for the intercession. The captain is gone. Viola, who realized that she was confused with Sebastian, rejoices in saving her brother.

On the street, Sir Andrew pounced on his adversary, whose timidity he had recently been convinced of, and gave him a slap in the face, but ... this is not a meek Viola, but a brave Sebastian. The cowardly knight is firmly beaten. Sir Toby is trying to intercede for him - Sebastian bares his sword. Appearing, Olivia stops the fight and drives her uncle. “Caesario, please do not be angry,” she says to Sebastian. She leads him into the house and offers to get engaged. Sebastian is bewildered, but agrees, the beauty immediately fascinated him. He would like to consult with Antonio, but he disappeared somewhere, he is not in the hotel. Meanwhile, the jester, pretending to be a priest, plays for a long time playing Malvolio sitting in the dark closet. Finally, taking pity, agrees to bring him a candle and stationery.

In front of Olivia's house, the Duke and Viola are waiting for a conversation with the Countess. At this time, the bailiffs brought Antonio, whom Viola calls the "savior", and Orsino - the "famous pirate." Antonio bitterly rebukes Viola for ingratitude, cunning and hypocrisy. Olivia appears from the house. She rejects the duke, and Cesario reproaches of infidelity. The priest confirms that he married the countess two hours ago with a ducal darling. Orsino is shocked. In vain Viola says that he has become her “life, light”, that he is “dearer to her than all women in this world”, nobody believes the poor thing.Then the beaten sir Toby and sir Andrew appear from the garden complaining of the ducal court Caesario, followed by an apology Sebastian (the unlucky couple again ran into a man). Sebastian sees Antonio and rushes to him. Both the captain and the duke are shocked by the similarity of the twins. They are completely at a loss. Brother and sister recognize each other. Orsino, realizing that the one who was so dear to him in the form of a young man, actually a girl in love with him, is completely reconciled with the loss of Olivia, who is now ready to consider her sister. He is impatient to see Viola in a female outfit: "... a virgin will appear before me, - / My soul is love and queen." The jester brings a letter to Malvolio. The oddities of the butler get an explanation, but Mary is not punished for a cruel joke - she is now a lady, Sir Toby, in gratitude for her tricks, married her. The insulted Malvolio leaves the house - the only gloomy character leaves the stage. The Duke orders "to catch up with him and to persuade the world." The play ends with a humorous melancholy song that Festa sings.