One year after the death of the Joker during the events of Arkham City, Batman is struggling to come to terms with the absence of his nemesis and the uncomfortable feeling that the pair shared a bond deeper than either could admit. Without the Joker's chaotic presence, Gotham's citizens have never felt safer, and crime in the city has dramatically declined. However, this gives Batman's enemies a chance to unite.
On Halloween night, Scarecrow threatens the city with his newly created strain of fear toxin and bombs planted throughout Gotham, forcing the evacuation of the city's six million civilians. Only criminals remain in the city, leaving Commissioner Gordon and the Gotham City Police Department outnumbered. Anticipating a new threat, Batman continues to develop crime-fighting technology and maintains a vigil over the city while, aided by the mysterious Arkham Knight, the Scarecrow unites Batman's greatest foes in a plot to finally destroy Batman.