[E]very reason excites to this, that my lady loves me . . . a kind of injunction drives to these habits of her liking...
In the garden of Olivia’s house, Sir Toby, Sir Andrew, and Maria—along with Fabian, one of Olivia’s servants—prepare to play their practical joke on Malvolio. Maria has written a letter carefully designed to trick him into thinking that Olivia is in love with him. She has been spying on him and knows that he is now approaching. She drops the letter in the garden path, where Malvolio will see it. She exits, while the three men hide among the trees and shrubbery.
Malvolio approaches on the path, talking to himself. He speaks of Olivia: it seems that he already thinks it possible that she might be in love with him. He is deep in a fantasy of what it would be like to be Olivia’s husband and the master of her house. He would have power over all the other servants and even over Sir Toby. Sir Toby and the others can’t help jeering at Malvolio’s pride from their hiding place, but they do it softly so that he will not overhear them and realize that they are there.
Malvolio spots the letter lying in the garden path. He mistakes Maria’s handwriting for Olivia’s, as Maria has predicted, and Malvolio thinks that the letter is from Olivia. Apparently, Maria sealed the letter with Olivia’s sealing ring to make the letter look even more authentic. To Sir Toby’s pleasure, Malvolio decides to read it aloud.
The letter is addressed to “the unknown beloved” and contains what seems to be a riddle about love (II.v.92). It suggests that the writer is in love with somebody but must keep it a secret from the world, though she wants her beloved to know about it. The first part of the letter concludes by saying that the beloved’s identity is represented by the letters M.O.A.I. Malvolio, naturally, works over the message in his mind until he has made it mean that he is the beloved (he notes, for instance, that all four of the letters appear in his own name). Sir Toby and the rest laugh at him from behind the bush.
Once he has convinced himself that Olivia is in love with him, Malvolio reads the second half of the letter. The mysterious message implies that the writer wishes to raise Malvolio up from his position of servitude to one of power. But the letter also asks him to show the writer that he returns her love through certain signs. The letter orders him to wear yellow stockings, “go cross-gartered” (that is, to wear the straps of his stockings crossed around his knees), be sharp-tempered with Sir Toby, be rude to the servants, behave strangely, and smile all the time. Jubilantly, Malvolio vows to do all these things in order to show Olivia that he loves her in return.
After Malvolio leaves, Sir Toby remarks that he “could marry this wench [Maria] for this device. . . . And ask no other dowry with her but such another jest” (II.v.158–160). Maria then rejoins the men, and she, Sir Toby, and Fabian have a good laugh, anticipating what Malvolio is likely to do now. It turns out that Olivia actually hates the color yellow, can’t stand to see crossed garters, and doesn’t want anybody smiling around her right now, since she is still officially in mourning. In other words, Malvolio is destined to make a great fool of himself. They all head off together to watch the fun.