After the overture, the Balladeer introduces the work and sings of the crimes of the notorious bandit and womanizer Macheath, Mack the Knife (“Ballad of Mack the Knife”). At the end of the song, Mack emerges from a group of prostitutes and strides across the stage.
In the shop of Jonathan Peachum (“Morning Chorale of JJ Peachum”), who controls and licenses London’s beggars, equipping and training them in return for a cut of their “earnings.” He enrolls a new beggar, then greets his wife, who has returned from a late night out. She learns that their grown daughter Polly, who was to have come home the previous evening, is not there. They argue over who is at fault for her absence (“‘What a Twat’ Song”). The scene shifts to the Savoy Hotel where Macheath and Polly are holding a reception after their wedding with his gang as attendants. The pastor arrives after some awkward banter, and the gang sings a crude “hymn” (“Wedding Song”). Polly responds with a song of her own (“Pirate Jenny”). The gang gets nervous when Chief of Police Tiger Brown arrives, but he is an old army buddy of Mack’s (“Cannon Song”) who has repeatedly saved him from arrest. Brown warns Mack not to interfere with the King’s forthcoming coronation, but he agrees to continue to protect Mack. He exits, Mack dismisses the gang, and Mack and Polly celebrate their marriage (“Love Song”). The scene shifts to Peachum’s shop, where he is reviewing the beggars and preparing them to impersonate patriotic veterans for the coronation. Polly enters and announces her marriage as her parents express dismay (“Barbara Song”); Mrs. Peachum reminds Polly of Mack’s fondness for prostitutes. Hoping to shut them up, Polly reveals Mack’s ties to Brown, which gives Mr. and Mrs. Peachum an idea about how to snare him. The trio meditates on the world’s corruption (“First Threepenny Finale: Concerning the Uncertainty of Human Relationships”).
Polly tracks down Mack on Tobacco Dock. His crimes are all over the news and she advises him to leave London. He assigns Polly the task of keeping the books for his bandit “business.” The gang enters and learns Polly will be in charge; skeptical at first, they soon accept her supremacy. Mack reluctantly reveals his secret to Polly: he has compromising documents that give him power over a member of the Royal Family. At last he exits, having promised Polly he will leave London immediately (“Melodrama” and “Polly’s Song”). Meanwhile Mrs. Peachum bribes the prostitute Jenny, Mack’s old lover, to turn him in (“Ballad of Lust and Desire”). The gang talks things over in the brothel; then Mack enters and Jenny tells his fortune, urging him to leave now. Mack and Jenny recall their old love (“Pimp’s Ballad”) as Jenny signals the police outside. They raid the brothel; Mack uses one of the prostitutes as a human shield, and she is shot to death before the police can arrest him. The entire cast comes onstage to sing the “Second Threepenny Finale.”
Macheath is in prison (“Ballad of the Free”). Brown tells him that he had no choice but to arrest him because he didn’t leave the country. After Brown exits, his daughter Lucy enters, followed almost immediately by Polly. Polly asks Mack to sign documents while Lucy insults her. The two women continue their fight (“Jealousy Duet”) as Macheath abandons efforts to placate them. Mrs. Peachum enters and takes Polly away. Lucy hands Mack his knife and helps him escape. Mr. Peachum comes to the jail, explains to Brown what has happened, and forces him once again to send the police after Mack.
As Peachum prepares the beggars for the coronation, Jenny comes to the shop to demand her bribe money, which Mrs. Peachum refuses to pay. As they argue, Peachum intervenes, breaking Jenny’s finger to force her to reveal that Mack is lying low in her room (“Ballad of Lust and Desire” reprise). When Brown arrives, determined to arrest Peachum and the beggars, Peachum explains that the beggars are posing as patriots for the coronation but prepared to revolt if Macheath is not hanged (“Song of Human Weakness”). Frustrated, Brown orders Mack arrested again; as he is brought to the police station, Jenny sings under a street light (“Solomon Song”). Polly and Lucy meet in the street and discover that they have some things in common. Mrs. Peachum enters and announces that Mack will be hanged. In his jail cell, Mack arranges to bribe one of the policemen (“Call from the Grave”). He begs the gang to raise the money, but they cannot; nor can Polly, who demands the compromising documents as their last hope. Mack is led to the gallows. Everyone, including Polly, tells him off, and he prepares to die (“Epitaph: Macheath Begs Forgiveness”). Then the Balladeer announces a deus ex machina. The king himself arrives to announce that Macheath has been pardoned and granted a pension (“Third Threepenny Finale”); then he takes possession of the compromising documents.