"9 months 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, including Penguin, Two-Face, and Harley Quinn, a chance to unite with the singular goal of killing 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 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."
- Excerpt from Batman: Arkham Knight's Wikipedia page, accessed August 13, 2020