Set in Victorian London, the play focuses on Macheath, an amoral, antiheroic criminal.
Macheath (Mackie Messer, or Mack the Knife) marries Polly Peachum. This displeases her father, who controls the beggars of London, and he endeavours to have Macheath hanged. His attempts are hindered by the fact that the Chief of Police, Tiger Brown, is Macheath's old army comrade. Still, Peachum exerts his influence and eventually gets Macheath arrested and sentenced to hang. Macheath escapes this fate via a deus ex machina moments before the execution when, in an unrestrained parody of a happy ending, a messenger from the Queen arrives to pardon Macheath and grant him the title of Baron.
The Threepenny Opera is a work of epic theatre. It challenges conventional notions of property as well as those of theatre. The Threepenny Opera is also an early example of the modern musical comedy genre. Its score is deeply influenced by jazz. The orchestration involves a small ensemble with a good deal of doubling-up on instruments (in the original performances, for example, some 7 players covered a total of 23 instrumental parts, though modern performances typically use a few more players). Its opening and closing lament, "The Ballad of Mackie Messer", was written just before the Berlin premiere, when actor Harald Paulsen (Macheath) threatened to quit if his character did not receive an introduction; this creative emergency resulted in what would become the work's most popular song, later translated into English by Marc Blitzstein as "Mack the Knife" and now a jazz standard that Louis Armstrong, Bobby Darin, Ella Fitzgerald, Frank Sinatra, Michael Bublé, Robbie Williams, Ray Quinn, and countless others have all covered. Another well-known song, recorded by Nina Simone, Judy Collins, and Marc Almond, is "Pirate Jenny", which was also recorded by Steeleye Span under the alternative title "The Black Freighter". The Pet Shop Boys, Tom Waits, and William S. Burroughs have recorded "The Second Threepenny Finale" under the title "What Keeps Mankind Alive?".