Don John is disappointed that his first attempt to sabotage Claudio and Don Pedro did not work: Claudio and Hero are still to be married. Borachio assures him he can disrupt the wedding with Don John's help. He suggests that Don John tell Claudio and Don Pedro that Hero is unfaithful. To counter their expected disbelief, Don John will lead them to a place below Hero's window on the night before the wedding. Then Borachio and his friend Margaret will appear at the window, making it look like Hero and another man are in an embrace. Borachio points out that the plot will have a fourfold impact: "to misuse the Prince, to vex Claudio, to undo Hero and kill Leonato." Don John promises to reward Borachio generously for his efforts if the plan works.
The audience has to imagine some of the unreported details of Borachio's plot. Although we accept that Borachio will be able to entice Margaret (his intimate friend for a year) to Hero's room and its window, how he will persuade her to act the role of Hero is unclear. Perhaps he will talk her into pretending that they are the happy couple about to be married. Margaret frequently uses words and ideas with sexual overtones, so enticing her into the window scene may not be difficult. Don John will tell the prince and Claudio that Hero loves Borachio, probably so that when they see him in the window, they will recognize him. Presumably, Margaret will be made to resemble Hero, at least at a distance.