Claudio is then led past Pompey and Overdone on his way to prison, and we learn what has happened to him. Claudio married Juliet, but they did not observe all the technicalities. Angelo, as the interim ruler of the city, decides to enforce a law that fornication is punishable by death, so Claudio is sentenced to be executed. Claudio's friend, Lucio, visits Claudio's sister, Isabella, a novice nun, and asks her to intercede with Angelo on Claudio's behalf.
Isabella obtains an audience with Angelo, and pleads for mercy for Claudio. Over the course of two scenes between Angelo and Isabella, it becomes clear that he lusts after her, and he eventually offers her a deal: Angelo will spare Claudio's life if Isabella yields him her virginity. Isabella refuses, but she also realizes that (because of Angelo's austere reputation) she will not be believed if she makes a public accusation against him. Instead, she visits her brother in prison and counsels him to prepare himself for death. Claudio desperately begs Isabella to save his life, but Isabella refuses. As a novice nun, she feels that she cannot sacrifice her own immortal soul (and that of Claudio, if he causes her to lose her virtue) to save Claudio's transient earthly life.
The Duke has not in fact left the city, but remains there disguised as a friar (Lodowick) in order to spy on the city's affairs, and especially on the actions of Angelo. In his guise as a friar, he befriends Isabella and arranges two tricks to thwart Angelo's evil intentions: