Betrayed by the whores, Macheath is freed from prison by the love of yet another woman.
- In the jail, Brown feels bad for having his friend Mac locked up.
- Mac writes a check to Smith to keep him from putting him in chains, and he sings about good living.
- Lucy comes to visit him and gives him a hard time for having married Polly Peachum.
- They argue until Polly herself comes to, and then it's a fight between all three of them that culminates in, you guessed it, another song.
- Mac denies that he's married to Polly, and Lucy announces she's pregnant with Mac's baby.
- Mrs. Peachum arrives and hauls Polly home.
- Mac promises to run away with Lucy and escapes from the cage.
- Peachum arrives, a little late, to get his reward for helping with the capture of Macheath, but realizes that Tiger Brown has let him get away.
- The curtain goes down and Macheath and Jenny sing a song about how humanity is actually really quite beastly.