A mood of self-indulgence prevails in Illyria. The Duke, Orsino, languidly pines for the love of Olivia, a noblewoman who has forsworn society to spend seven years mourning her dead brother. Contrary to Olivia’s assumed somberness, frivolity reigns in her house. Her uncle, Sir Toby Belch, presides over drunken riots attended by Sir Andrew Aguecheek, a rich but foolish knight whose wooing of Olivia Toby encourages for the financial benefits it affords himself, Olivia’s gentlewoman, Maria, and gentleman, Fabian. Soon Feste the Clown reappears to join their number. Against this confederacy stands Olivia’s steward, Malvolio, a man who confuses self-righteousness for virtue and self-importance for dignity. Into this community is cast a young gentlewoman named Viola. Survivor of a shipwreck that she believes has killed her twin brother (who lives on in her looks), Viola must make her own way amid unknown surroundings. To this end, she dons male dress and enters the service of Orsino under the name Cesario. But however successfully her masculine costume deceives the eyes of those she meets, it cannot fool her own heart; she falls in love with the Duke her master.
Soon, Viola has gained Orsino’s confidence to the extent that the Duke trusts “him” to act as his envoy to Olivia. Viola performs this office with great vigor and good humor, with the unfortunate result that Olivia immediately falls in love with “Cesario.” Her vows forgotten, Olivia resorts to devious means to lure “him” back. Meanwhile, Viola’s brother, Sebastian, also arrives on the seacoast. Unaware of Viola’s survival, he has been rescued by Antonio, a sea captain. A great bond has grown between them, so Antonio braves his enemies to follow Sebastian to Illyria and lends him money. After the puritanical Malvolio scolds Sir Toby and his cohorts, Maria plots their revenge on the steward. Playing on Malvolio’s vanity, she forges what appears to be Olivia’s confession of love for him. His mind already teeming with such fantasies, he unsceptically peruses the letter and sets out to follow its apparent commands. Far from entertaining any such affection for her servant, Olivia in fact admits to Cesario that she loves “him.” Viola can do nothing but repeat her ironic statement that she’ll never love any woman, but Olivia persists.
Even while Olivia continues in this state of agitation, Malvolio appears before her, wearing yellow stockings, cross-gartered, and smiling madly. Unaware that he acts according to the spurious information in the letter, Olivia fears he’s lost his mind. She turns him over to the “care” of Sir Toby, which results in his being bound, put into darkness, and forced to endure an absurd interview with the curate, actually the Clown disguised. Having observed Olivia’s behavior toward “Cesario,” Sir Andrew is prepared to give up his suit. Eager to keep Sir Andrew’s purse at hand, Sir Toby persuades the foolish knight that a challenge to Cesario is the way to attract Viola. Neither combatant is particularly eager to fight, even less so after Sir Toby and Fabian exaggerate their opponents’ prowess. Still, it looks as if some sort of duel will occur when Antonio arrives on the scene.
Mistaking the disguised Viola for Sebastian, he steps in the fray, only to be arrested for his past naval exploits against the fleet of Orsino. Not knowing Antonio, and unable to succor him, Viola nevertheless departs with new hope that her brother lives. Sebastian enters almost immediately, and is baffled when the local inhabitants seem to recognize him. He exchanges words with the Clown, blows with Sir Andrew, and is about to fight Sir Toby when Olivia appears. Olivia fills him with wonder. She leads him away, pleased to find “Cesario” suddenly tractable, and they secretly marry. Informed of the appearance of Antonio by Viola, Orsino and his retinue arrive at Olivia’s house.
Antonio admits to his past acts against Orsino, but confuses his listeners by calling on Viola. Olivia arrives, reiterates her refusal of Orsino, and also mistakes Viola for Sebastian, chastising Cesario for “his” absence. Orsino falls into a jealous rage because Olivia prefers his servant to himself, and makes to depart, Viola following obediently. But to her own amazement, Viola is charged first with having married Olivia and then with having hurt Sir Toby and Sir Andrew. With matters so hopelessly confused, the appearance of Sebastian is a revelation. The joy of the twins’ reconciliation is shared not only by Sebastian’s bride, Olivia, but also by Orsino, who finally recognizes the true nature of Viola’s affection for him, and agrees to marry her. Only the bitter departure of the ridiculous but ill-used Malvolio mars the festive atmosphere; some always find romance and the virtues it inspires — good humor, wonder, and especially, sympathy — intolerable.