Faced with overwhelming poverty and a pregnant wife, a tragic, struggling comedian is forced to turn to crime. In his first heist, he is immersed in toxic chemicals that disfigure him bizarrely, driving him mad and thus giving birth to The Joker.

For years, the Clown Prince of Crime has been caught in a dance of violence with his greatest nemesis, the Batman. Escaping Arkham Asylum, he plots his most lethal caper. This will be the ultimate punch line... his Killing Joke.

In their mission to protect Gotham City, Batman and Batgirl (Barbara Gordon) pursue ruthless criminals such as the grandiose Maxie Zeus and Antonio "Python" Palmares. Simultaneously, Commissioner James Gordon and Detective Harvey Bullock take on a cartel distributing the latest designer drug-"giggle sniff," derived from a venom created by The Joker.

This rapid-fire sequence of events spirals together to threaten Batman's closest friends and allies, and locks the two eternal foes in their ultimate death match.