Twelfth Night — Act 2, Scene 5: OLIVIA's garden.

Sir Toby, Sir Andrew, and Fabian hide in Olivia’s garden to watch Malvolio walk in, already proud of himself and imagining that Maria loves him. Maria has planted a fake love letter and slips away so the others can see him read it. Malvolio finds the letter, believes it is in Olivia’s hand, and becomes convinced that Olivia secretly desires him. He studies the strange initials and directions, then decides to obey the instructions by changing his behavior. He leaves determined to wear yellow stockings, cross-garters, and a big smile. The others revel in the prank, and Maria returns to hear that it has worked.