The Duke of Vienna, Vincentio, leaves the city on a diplomatic mission. While he is away, he places Vienna in the care of his subordinate, Angelo, who decides to tighten the city’s anti-fornication laws. A young nobleman, Claudio, has sex with his wife-to-be, Juliet, before they are married, and Angelo decides to execute him as punishment. Claudio’s sister Isabella, a nun, tries to save him, but Angelo will only save Claudio should she sleep with him, which she refuses to do. The Duke has not really left the city, and is disguised as a friar in order to see what would happen if he did leave, and in order to expose Angelo, he tricks him twice. First, he makes Angelo think he is sleeping with Isabella, when he is really sleeping with Mariana, with whom he was supposed to be married. Second, when Angelo asks for Claudio’s head, the Duke provides a head of a lookalike. When the Duke decides to reappear, Isabella and Mariana petition him to punish Angelo. Angelo tries to weasel out of things by blaming his actions on the friar, who was really the Duke in disguise. The Duke reveals himself to be the friar, and Angelo is punished by being forced to marry Mariana. Likewise, Claudio’s friend Lucio, for slandering the Duke and the friar, who were the same man, is forced to marry a whore.