Batman is lured back into Arkham City by its last remaining super-criminal; Harley Quinn. Now more dangerous than ever, she wants her revenge! This expansion adds a couple of hours of new content and the possibility to play both as Batman and as Robin.

Harley Quinn's Revenge begins with Robin searching for Batman, who has disappeared while infiltrating Harley’s headquarters in the Industrial District to free several cops that Harley has kidnapped. During the search, Oracle confides in Robin that she’s worried about Bruce, who hasn’t been the same since the Arkham City incident and refuses to talk about Talia or Joker. Eventually Robin discovers Batman's Utility Belt, discarded. The story rewinds to two days earlier, where Batman learns from Gordon that Harley has taken several officers hostage. Before Batman leaves, Gordon warns him that Harley still blames him for Joker’s death, and that it could be a trap. Batman rescues one cop from the Steel Mill, who tells him that the others were dragged elsewhere. After attaining location and access codes to Harley’s secret base, Batman infiltrates the shipping yard and attempts to rescue another cop, but is rendered unconscious when Harley attempts to shoot the officer, which Batman intercepts. One of Harley’s thugs removes Batman’s belt, only to drop it when the belt’s countermeasures electrocute him, leaving it for Robin to find.