Pompey takes a look around the prison and declares that he feels like he's at his workplace, Mistress Overdone's brothel. (In other words, most of Overdone's customers are now in jail.)
Abhorson calls Barnardine out of his cell and announces that it's time for him to be executed.
Barnardine says he was partying and drinking all night, so he's not fit to be executed right now –on account of his terrible hangover.
Pompey says the best cure for a hangover is a good hanging because it allows one to sleep it off… permanently.
The Duke arrives in his friar disguise and offers to pray with Barnardine before he dies.
Barnardine says he's not feeling well enough to be executed and says he's going back to his cell, but thanks anyway.
The Duke orders Pompey and Abhorson to take Barnardine to the chopping block.
The Duke complains to the Provost that Barnardine isn't prepared for death and it would be a "damnable" sin to execute a man who isn't ready to die.
Duke Vincentio is upset because his plan to substitute Barnardine's head for Claudio's doesn't seem like it will work out. Then, though, the Provost reveals that a pirate who looks like Claudio just died in the prison that morning – they can cut off his head and send it to Angelo. (Gee. What a strange coincidence.)
The Provost runs off to hide Claudio so Angelo won't know he's being scammed.
The Duke writes Angelo a letter announcing that he'll be back in town soon and that Angelo should meet him at a fountain in Vienna.
The Provost returns with Ragusine's head (we now have a name for the conveniently dead pirate who looks just like Claudio) and runs off to deliver it to Angelo.
Isabella enters the prison asking about her brother.
For some reason, the Duke decides it's a good idea to lie and say that, sadly, Claudio has been executed.
Isabella is crushed, but the Duke calms her down by promising that he has a plan to punish Angelo.
The Duke gives Isabella a letter to deliver to Friar Peter and promises her that she'll be able to lodge a complaint with the Duke who is due back in Vienna any day now. Isabella should meet with him at Mariana's house later that night.
Lucio enters and declares that, if Duke Vincentio hadn't run off to some secret hiding place, he, the Duke never would have allowed Claudio to be executed.
Lucio confesses that he once got a girl pregnant, but denied it when he was taken to court. As a result, he got off the hook without having to marry her.