Sir Andrew suggests challenging Malvolio to a duel, but Maria has a better idea: to play a practical joke on him. As she explains to Sir Toby and Sir Andrew, Malvolio is a puritan, but at the same time his biggest weakness is his enormous ego: he believes that everybody loves him. Maria will use that weakness to get her revenge on him for spoiling their fun. Since Maria’s handwriting is almost identical to Olivia’s, Maria plans to leave letters lying around that will appear to have come from Olivia and will make Malvolio think that Olivia is in love with him.
Sir Toby and Sir Andrew are amazed by Maria’s cleverness, and they admire the plan. Maria goes off to bed, planning to get started on her joke the next day. Sir Toby and Sir Andrew, deciding that it is now too late to go to sleep, head off to warm up more wine.