Olivia and Maria are in the garden, and Olivia is making plans to entertain Cesario; she sent him an invitation, and he has promised to come to visit her. She is very excited at the prospect and wonders how to treat him, how to "feast him." She is afraid that he will think that she is trying to "buy" him. Where is Malvolio, she wonders; he is usually grave and polite and can be counted on to calm her nerves.
Smiling foolishly, Malvolio enters. His whole appearance has changed since we last saw him; his dark clothes are gone, as is his dour appearance. Maria's forged love note has changed him from being "sad and civil" into being a merrily smiling fabrication of a courtier; he complains a bit about the cross-gartering causing "some obstruction in the blood," but he suffers gladly — if it will please Olivia. Smiling again and again, he kisses his hand and blows his kisses toward Olivia. She is dumbfounded by his unexplainable, incongruous dress and behavior, but Malvolio doesn't seem to notice. He prances before her, quoting various lines of the letter which he supposes that Olivia wrote to him, and in particular, he dwells on the "greatness" passage. Olivia tries to interrupt what he is saying, but to no avail; he rambles on and on until she is convinced that he must be suffering from "midsummer madness."
A servant announces the arrival of Cesario, and Olivia places the "mad" Malvolio in Maria's charge; in fact, she suggests that the whole household staff should look after him. Meanwhile, Malvolio, remembering the orders which Maria inserted into the letter, spurns Maria, is hostile to Sir Toby, and is insulting to Fabian. He finally drives them all to exasperation and fury, and when he leaves, they make plans to lock him up in a dark room, a common solution for handling a lunatic in Elizabethan days. Olivia won't mind, says Sir Toby: "My niece is already in the belief that he's mad."
Sir Andrew enters, and he carries a copy of his challenge to Cesario. He is exceedingly proud of the language, which, we discover as Sir Toby reads it aloud, is exceedingly stilted and obtuse and, in short, is exceedingly ridiculous. Sir Andrew's spirits are high, and Maria decides that the time is ripe for more fun: she tells him that Cesario is inside with Olivia. Sir Toby adds that now is the time to corner the lad and as soon as he sees him, he should draw his sword and "swear horrible." According to Sir Toby, "a terrible oath, with a swaggering accent sharply twanged off, gives manhood." Offering his services, Sir Toby says that he will deliver Sir Andrew's challenge "by word of mouth." He is sure that Cesario, clever young man that he is, will instantly see the harmless humor in the absurdly worded challenge; it couldn't possibly "breed . . . terror in the youth." And thus the practical jokers exit — just as Olivia and Cesario enter.
This scene-within-a-scene is very much like ones we have already witnessed: Cesario pleads that his master, Duke Orsino, should be considered a serious suitor, and Olivia changes the subject to Cesario himself, as she gives him a diamond brooch containing a miniature portrait of herself. Cesario accepts it politely and courteously, and Olivia exits.
Sir Toby and Fabian enter and stop Cesario before he can leave for Orsino's palace. Sir Toby tells Cesario that Sir Andrew, his "interceptor," is waiting for him and is ready to challenge him to a sword fight. Cesario panics (remember that he is Viola, who knows nothing of violence and dueling). Sir Toby continues: Sir Andrew is a "devil in a private brawl," for he has killed three men already ("souls and bodies hath he divorced three"). Cesario, says Sir Toby, can do only one thing to defend himself against Sir Andrew: "strip your sword stark naked." Such advice is alarming. Cesario begs Sir Toby to seek out this knight and find out what offense he has committed, and so Sir Toby exits, ostensibly to go on his assigned errand, leaving Cesario in the company of Signior, a title Sir Toby impromptly bestowed on Fabian, all in the spirit of their practical joking. These two exit then, just as Sir Toby and Sir Andrew enter.
Sir Toby describes in vivid, violent language Cesario's fierceness. Sir Andrew quakes: "I'll not meddle with him"; he is even willing to give Cesario his horse, "grey Capilet," to avoid the duel. Fabian and Cesario return, and Sir Toby taunts both Cesario and Sir Andrew into drawing their swords, all the while assuring them that no real harm will come to either of them.
At this point, a true swordsman enters. It is Antonio, and mistaking young Cesario for Sebastian, he tells Sir Andrew to put up his sword unless he wants to fight Antonio. Sir Toby draws his sword and is ready to take on Antonio when a troop of officers enters. Antonio has been recognized on the streets, and Orsino has sent out his men to arrest him. Dejectedly, Antonio turns to Cesario (who he believes to be Sebastian). He asks him for his purse back, and when Cesario naturally denies having ever received it, the sea captain is both saddened and enraged by this apparent ingratitude. He denounces this youth, "this god," whom he "snatched . . . out of the jaws of death . . . [and offered the] sanctity of love." "Sebastian," he tells Cesario, "thou . . . virtue is beauty, but the beauteous-evil / Are empty trunks o'erflourished by the devil."
As the officers lead Antonio away, Viola is almost ready to believe what may be possible: Sebastian may be alive! It is possible that this man saved her twin brother, Sebastian, and Antonio may have just now confused her with Sebastian because of her disguise. Breathlessly, she prays that "imagination [should] prove true / That I, dear brother, be now ta'en for you." Viola exits, and unwilling to miss their fun, Sir Toby and Fabian easily convince old Sir Andrew that Cesario is a coward, and the three of them set out after Orsino's page.
This scene is not only the longest scene in the entire play, it is also longer than the entirety of Act IV and the entirety of Act V. Likewise, there are many divisions within this scene in terms of several different groupings of characters on the stage and several uses of mistaken identities. Malvolio is mistaken for a madman by Olivia, Olivia is mistaken for a true love by Malvolio, Viola is mistaken for a man who allegedly insulted Sir Andrew, Viola is mistaken for a man with a "heart of stone" by Lady Olivia, and Viola is mistaken for her brother Sebastian by Antonio.
Before Malvolio arrives, Maria warns Olivia (and the audience) that Malvolio is "possessed," that he is out of his mind and that his sanity has been taken over (possessed) by devils. When Malvolio does appear, we are not disappointed. As in other scenes in Twelfth Night, the staging is an extremely important part of the total effect. As Maria goes out and returns, ushering in Malvolio, the change in the steward is dramatic. Instead of being "sad and civil," he smiles broadly and continually; he kisses his hand to the Lady Olivia, and instead of being dressed in sober black, he is in yellow stockings with tight cross-garters in a contrasting color. Malvolio keeps on referring to various lines of the letter which he supposes that Olivia wrote to him, but since Olivia did not write the letter, she has no idea what he is talking about. Furthermore, Olivia does not realize that Malvolio is quoting; she assumes his talk to be the ravings of a madman, and she wishes that he would leave her sight and be treated for his madness.
Meanwhile, on the stage, the only one present who does know what Malvolio is referring to is Maria, who is probably behind Malvolio laughing uproariously. Knowing the contents of the letter (since she wrote it), Maria very cunningly asks Malvolio some questions that cause him to continue quoting from the letter; this, of course, heightens the impression that he is raving.
As Malvolio insists on quoting line by line from the letter, and as he returns time after time to the "greatness" passage, Olivia becomes more and more confused, for she thinks that he is madly rambling. Finally, feeling compassion for her steward, she thinks that "this is very midsummer madness."
Sir Toby's delight in practical jokes is again illustrated as he plans some good sport between Sir Andrew and Cesario (Viola). He is, of course, working always under the assumption that no harm will come to either party since the challenge and his arrangements will "so fright them both that they will kill one another by the look, like cockatrices." Sir Toby, of course, is right. The duel between Sir Andrew Aguecheek and Cesario (Viola) is one of the high points of the comedy of this play. Equally absurd is the fact that the pretended duel is fought over Lady Olivia, whom Cesario (Viola) has rejected and who is not even aware of the foolish Sir Andrew's intentions. In fact, part of the high comedy involves the egotistical absurdity of Malvolio's thinking that the high-born Lady Olivia would stoop to love him and, in addition, the foolishness of Sir Andrew's thinking that he has enough of a romantic chance with this lady to enter into a duel upon her behalf. The absurdity of Sir Andrew's and Cesario's dueling for the love of Olivia is one of the most ludicrous duels in the history of the stage. Then to add to the absurdity, Antonio comes on stage to defend "Sebastian" (Viola disguised as Cesario) and finds himself dueling with the fat, belching Sir Toby.
The various elements of the plot are slowly being brought together. Viola now realizes that she has been mistaken for her brother, thereby preparing the way for Sebastian to be mistaken for her by the Lady Olivia.