The Duke visits Mariana and is there when Isabella arrives. Isabella says that Angelo gave her two keys and instructions to meet him in a garden. Angelo showed her the way twice. She told Angelo that a servant will be accompanying her, thinking that she is coming to speak about her brother, so she cannot stay long.
Duke introduces Mariana to Isabella and tells them to discuss the plans together on their own. They go for a walk, and when they return they have agreed on the plan. Isabella tells her to say very little, but to be sure to tell him, "Remember now my brother," before she leaves. The Duke tells Mariana that she is not committing a sin, since she and Angelo had a contract of marriage.
Meanwhile, back at the prison, the Provost asks Pompey if he will help execute Claudio and another prisoner. If he does so, the charges against him will be dropped. Pompey agrees, and the Provost introduces him to Abhorson, the executioner. Abhorson says that Pompey will discredit the execution trade. Pompey agrees to be his helper, though, and Abhorson is told to be ready at four o'clock the next day.
The Duke arrives, and the Provost asks if there is any hope of saving Claudio. The Duke says that a pardon may arrive before morning. A messenger arrives, and the Duke says that it is probably the pardon, but it contains instructions to execute Claudio by four o'clock and Barnadine in the afternoon, and to send Claudio's head to Angelo by five.
The Duke asks who Barnadine is, and the provost tells him that he is a Bohemian who has been in prison for nine years. The Duke asks whether he is repentant, and the Provost says that he is as reckless and carefree as he has always been. The Provost says that he does not care that he is in prison, and has not been affected by news of his upcoming execution.
The Duke asks for Claudio's execution to be postponed four days. The Provost asks how he could do such a thing, considering the precision of Angelo's instructions. The Duke tells the Provost to send the head of Barnadine in place of Claudio's. The Provost argues that Angelo will notice it is the wrong person, but the Duke tells him to shave the head and beard of Barnadine's head to disguise it.