The events of Arkham City are set one year after Batman: Arkham Asylum. Quincy Sharp, the asylum's erstwhile director, has taken sole credit for halting the Joker's armed siege, using this distinction to become mayor of Gotham City. Declaring both the asylum and Blackgate Penitentiary no longer suitable to contain the city's detainees, Sharp's administration orders both facilities closed and he purchases Gotham's most notorious slums, converting them into an immense prison enclosure known as Arkham City. This facility is subsequently placed in the care of psychiatrist Hugo Strange—who is secretly manipulating Sharp—and monitored by a rogue private military firm, TYGER Security. Strange permits the inmates to do as they please, so long as they do not attempt to escape. A wary Batman maintains his own vigil over the new project, concerned that the chaotic situation there will get out of hand. Meanwhile, the Joker is suffering from a potentially fatal disease caused by his previous consumption of the Titan formula, an unstable steroid serum which turns men into maddened monsters.
