Lady Olivia.
Act III.
Cesario has another private meeting with Lady Olivia on Duke Orsino's behalf.
Sir Toby and Sir Andrew meet Cesario (Viola) and Sir Toby learns from Cesario that he will soon speak with Lady Olivia. In private, Lady Olivia admits to Cesario that she used the ring she sent after him to lure him back to her.
Cesario (Viola) tries to put Olivia off him but she is smitten, ignoring all Cesario's attempts to diminish her enthusiasm for "him"...
Knowing Lady Olivia will never love him, Sir Andrew prepares to head for home. The sight of Olivia showing more affection to a youth (Cesario) than him was the last straw.
Fabian and Sir Toby don't deny the affectionate display but argue Olivia did it to spur Sir Andrew to woo her and regain her respect. Sir Toby and Fabian manipulate Sir Andrew into writing a challenge to the youth (Cesario) even though they know a fight between two cowards (Cesario and Sir Andrew) is unlikely.
Maria enters, telling Sir Toby and Fabian to watch the spectacle that is Malvolio wearing yellow stockings and being cross-gartered.
Sebastian has now reluctantly accepted Antonio as his companion in the streets of Illyria.
Antonio explains that his offence in Illyria, which was theft, was one the rest of his city have repaid but he has not and so he is still wanted in Illyria. Sebastian decides to look around, but Antonio fearful of his enemies, decides to head for lodging at a place called "the Elephant." Antonio gives Sebastian his purse (wallet) and directions to this lodging and the two part their separate ways...
Olivia makes plans to once more woo Cesario (Viola). Olivia sees Malvolio with yellow stockings and cross-gartered and considers him mad since he continues to smile no matter what the situation and makes crude, lustful interpretations of Olivia's words.
Malvolio makes his famous "'Some are born great,'-" speech.
Learning that Cesario has returned, Lady Olivia has Malvolio put into the care of her servants since in her eyes, Malvolio's behavior is some "midsummer madness."
Sir Toby, Maria and Fabian plot to have Malvolio placed in a "dark room," so they can have some fun with him. Sir Andrew arrives with his completed letter challenging Cesario. Sir Toby decides to verbally scare Cesario and Sir Andrew about their opponents instead of sending the letter.
Alone with Cesario once more, Lady Olivia makes no progress with Cesario who will not requit (return) her love. Olivia is undaunted by this. Sir Toby scares both Sir Andrew and Cesario into drawing their weapons on each other.
Antonio arrives, pledging to fight Sir Andrew on Cesario's (Viola's) behalf who he thinks is Sebastian since Viola disguised as a man now looks like her twin brother Sebastian.
The fight is stopped but Officers recognizing Antonio, capture him. Antonio asks Cesario (Viola) for his purse back but Cesario not recognizing him does not oblige.
Antonio thinks Sebastian has betrayed him, not realizing he has asked Cesario (Viola) for his purse, not Sebastian.
Act IV.
Confusion reigns as Sebastian is now mistaken for Cesario when Feste insists Sebastian sent for him and Sebastian is certain he did not (Cesario obviously did).
Sir Andrew finds Sebastian and thinking it is Cesario from the earlier "fight" that did not happen, hits Sebastian. Sebastian unlike Cesario is not afraid to return the favor and a fight is only stopped by Sir Toby's intervention. Sir Andrew decides to have Sebastian punished by the law of Illyria despite the fact that he started the fight.
Sir Toby and Sebastian are just about to fight when Olivia screams for her uncle, Sir Toby to stop. Olivia now scolds Sir Toby, hoping Sebastian, whom she thinks is Cesario (Viola), will forgive her uncle and not be displeased with her.
Sebastian, amazed that this beautiful woman he does not know, loves him, replies to Olivia that he will be ruled by her and the two set off to marry immediately...
In Olivia's house, Malvolio in a darkened room is teased mercilessly by Feste who tries unsuccessfully to convince Malvolio that he is mad.
Sir Toby, fearing that his fight with Cesario (actually Sebastian) has put him on thin ice with Olivia, wants Feste's teasing of Malvolio to stop. Feste has other ideas but eventually lets Malvolio write a letter to Olivia proclaiming his sanity...
Sebastian can barely believe his luck, a beautiful woman (Olivia) loves him and has given him a pearl. Sebastian briefly wonders if he is dreaming before he marries Olivia in a private chapel. Olivia explains that their now secret marriage will be revealed later...
Act V.
In the final scene, chaos ensues as the identical appearing Cesario (Viola) and Sebastian are each blamed for the other's actions. First Feste blames Sebastian for beckoning him, not realizing it was Cesario who called for him.
Cesario spots Antonio the man who saved him from fighting Sir Andrew but was taken prisoner by Orsino's officers in Act III. Antonio again asks Cesario for his wallet back thinking he is Sebastian. Cesario (Viola), who does not know Antonio, does not and so Antonio curses him for his betrayal, not realizing he is talking to Cesario not Sebastian whom he lent his wallet to.
We learn that Antonio is an enemy of Illyria and especially of Orsino for plundering his ships as a pirate in the past.
Now a prisoner, Antonio baffles Orsino by telling him that he and Cesario (Viola) have been together night and day for three weeks when who Antonio is really thinking of is Sebastian. Orsino cannot believe this; Cesario has been with him for three weeks.
Olivia arrives and we see that Orsino still loves her. The feeling is not mutual... Olivia scolds Cesario (Viola) for neglecting her, revealing that "he" is her husband.
Cesario (Viola) amazed by this, pleads "his" innocence to Orsino who "he" truly loves and Orsino thinking his servant betrayed him by taking Olivia for himself, prepares to punish Cesario.
Olivia meanwhile despairs that her husband Cesario who really is Sebastian, would leave willingly with Orsino to be punished rather than be with his wife and she too claims betrayal by Cesario (Viola).
Sebastian arrives, apologizing for attacking Sir Toby and Sir Andrew. Orsino seeing both Cesario and Sebastian together is amazed that he sees two copies of the same man. Olivia too is amazed.
Sebastian and Cesario compare notes on how they arrived in Illyria each claiming that their sibling had drowned.
Eventually they realize that since they knew the same father they are indeed brother and sister, Cesario revealing "his" real identity as the woman named Viola.
Malvolio storms in and the cruel prank against him is revealed by Fabian who confesses.
Orsino calls Olivia his sister, and Orsino takes Cesario for his mistress and we presume later his wife with Feste ending the play in song.