At Olivia's house, Sir Toby Belch, Olivia's uncle, is criticizing his niece for mourning the death of her brother so profusely. He says to her serving girl, Maria, that his niece is melodramatically overreacting, and he thoroughly disapproves. Maria disapproves of several things herself: she disapproves of Sir Toby's arriving at such a late hour, dressing so slovenly, and drinking so much. Only yesterday, Olivia complained of these things, plus the fact that Sir Toby brought someone who he thinks is the perfect suitor to the house, Sir Andrew Aguecheek. Despite Maria's calling Aguecheek a "fool and a prodigal," Sir Toby is proud of the chap — a fitting suitor for his niece: Aguecheek, he says, receives three thousand ducats a year, plays the violincello, and speaks several languages. Maria is not impressed. To her, the man is reputed to be a gambler, a quarreler, a coward, and a habitual drunkard.
When Sir Andrew joins them, there follows a brief exchange of jests, most of them at Sir Andrew's expense. Maria leaves, and the two men discuss Sir Andrew's chances as a prospective suitor of Olivia. Sir Andrew is discouraged and ready to ride home tomorrow, but Sir Toby persuades him to prolong his visit for another month, especially since Sir Andrew delights in masques and revels and, as Sir Toby points out, Sir Andrew is a superb dancer and an acrobat, as well. Laughing and joking, the two men leave the stage. It is obvious that Sir Toby has a secret and mysterious purpose for wanting to persuade Sir Andrew to stay and woo the fair Olivia.
With this scene, we are introduced to still another set of characters: in the modern idiom, we have already met the "upstairs" characters; now we meet the "downstairs" characters. Sir Toby Belch, Sir Andrew Aguecheek, and Maria form the subplot that counterbalances the main plot. Sir Toby Belch, as his name implies, is characterized by his heavy drinking and by his obese, corpulent frame. In an earlier play, Shakespeare created a similar type of character in Sir John Falstaff (See Henry IV, Part I and Part II); this character was extremely popular with Elizabethan audiences, and Sir Toby is reminiscent of the earlier Sir John; both are plump, jolly knights with a penchant for drinking, merrymaking, and foolery of all types. In this play, Sir Toby spends most of his time complimenting Sir Andrew so that the latter will continue to supply him with money for drinking and cavorting. Sir Toby's niece, we discover, is too withdrawn in her melodramatic mourning to be aware of the partying going on in her house, but when she does become aware of it, she disapproves and relies upon her steward, Malvolio, to keep her household in order; thus, Malvolio will soon become the butt of the partymakers' jokes.
Maria, another member of the subplot, is Olivia's vivacious, clever, and mischievous maid. She comes from a Shakespearean tradition of servants who are wittier and cleverer than the people who surround them. Thus, she will be seen to be far more witty than Sir Andrew Aguecheek is, and he will become the object of her many jokes and puns, but he will never realize the extent to which Maria ridicules him.
Sir Andrew Aguecheek is necessary for the plot mainly because he is in possession of three thousand ducats a year, and Sir Toby is anxious to remain on good terms with him so as to be a recipient of the eccentric knight's beneficence. Consequently, he continually plots ways to make the knight think that Olivia is indeed receptive to the romantic overtures of the tall, skinny, ridiculous knight. Now we know that two vastly different people, Duke Orsino and Sir Andrew Aguecheek, are both seeking the hand of the Lady Olivia. Later, Malvolio will become a third "suitor," by a ruse played upon him by Maria and her cohorts.