Nine months after the death of the Joker during the events of Arkham City, Batman is struggling to cope with the absence of his archenemy and the uncomfortable feeling that the pair shared a bond deeper than either could admit. Without the Joker's presence, Gotham's citizens have never felt safer, and crime in the city has declined significantly. However, this gives Batman's enemies, including Penguin, Riddler, Two-Face, and Harley Quinn, a chance to unite with the singular goal of defeating Batman. Having anticipated a new threat, Batman has continued to develop crime-fighting technology and maintain a vigil over the city. On Halloween night, Scarecrow, who Batman had defeated in Arkham Asylum, 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.