Pompey remarks that he is as well acquainted with the prison as with Mistress Overdone's brothel. He adds that many of the same people frequent both places, and lists them.
Abhorson enters, telling Pompey to bring Barnadine. Barnadine tells them that he has been drinking all night and does not want to die today. The Duke comes to offer prayer, and Barnadine holds firm, saying that he will not die.
The Provost tells the Duke that a notorious pirate, of about Claudio's age, died in prison the night before, and that they can use his head instead of Barnadine's. The Duke says that it "is an accident that heaven provides" (IV.iii.76). He tells the provost to hide both Barnadine and Claudio and send the head immediately to Angelo.
Isabella enters, asking if the pardon has arrived. The Duke tells her that her brother has already been executed, his head sent to Angelo. Isabella wants to go to Angelo, but the Duke tells her that she will not be admitted. Instead, he says, she should wait until the Duke's return and have Angelo punished by his superior. He gives her a letter to take to Friar Peter.
Lucio enters and tells Isabella that he is mourning her brother's death. He also says that if the Duke had been in Vienna, Claudio would not have died. Isabella exits, and Lucio begins to talk about the Duke's relations with women again. The Duke says that he does not want to hear more stories. Lucio tells him that he was once before the Duke for impregnating a woman, but that he denied it because he did not want to marry her.
Angelo and Escalus discuss the Duke's letter. They do not understand why they have to meet him at the gates. The letter also orders them to proclaim that anyone with a complaint should present a petition in the street, ostensibly to ensure that no one lodges a complaint against Angelo later on. Escalus leaves, and Angelo wonders what Isabella might say. He hopes that she will be too modest to tell what has happened. He also says that he would have let Claudio go, but was worried about later revenge.