A gang of criminals rob a Gotham City mob bank, double-crossing and murdering each other until there is only one left: The Joker, who escapes with the money.
Batman, District Attorney Harvey Dent and Lieutenant Jim Gordon form an alliance to rid Gotham of organized crime. Bruce Wayne is impressed with Dent’s idealism and offers to support his career; he believes that, with Dent as Gotham’s protector, he can give up being Batman and lead a normal life with Rachel Dawes—even though she and Dent are dating.
Mob bosses Sal Maroni, Gambol and the Chechen hold a videoconference with corrupt accountant Lau, who has taken their funds and fled to Hong Kong. The Joker interrupts, warns them that Batman is unhindered by the law, and offers to kill him in exchange for half of their money, but Gambol puts a bounty on the Joker instead after he insults him. After escaping and smuggling himself as a corpse, the Joker kills Gambol and takes over his gang. The mob ultimately decides to take the Joker up on his offer.
Dent arrests the entire mob, while Batman finds Lau in Hong Kong and brings him back to Gotham to testify against them. The Joker threatens to keep killing people unless Batman reveals his identity, and starts by murdering Police Commissioner Gillian B. Loeb and the judge presiding over the mob trial. The Joker also tries to kill Mayor Anthony Garcia, but Gordon sacrifices himself to stop the assassination. Dent learns that Rachel is the next target.
Bruce decides to reveal his secret identity. Before he can, however, Dent announces that he is Batman. Dent is taken into protective custody, but the Joker appears and attacks the convoy. Batman comes to Dent’s rescue and Gordon, who faked his death, arrests the Joker and is promoted to Commissioner. Rachel and Dent are escorted away by Michael Wuertz and Anna Ramirez, detectives on Maroni’s payroll. Batman interrogates the Joker, who reveals that Rachel and Dent have been trapped in separate locations rigged with explosives. Batman races to save Rachel, while Gordon goes to save Dent. Batman arrives at the building, realizing that the Joker sent him to Dent’s location instead. Both buildings explode, killing Rachel and disfiguring half of Dent’s face. The Joker escapes the jail with Lau.