The best news about Batman: Arkham City is that it's a sequel that lives up to and even surpasses the original. The story takes place 18 months after the original game. Quincy Sharp, the onetime administrator of Arkham Asylum, has become mayor and convinced Gotham to create "Arkham City" by walling off the worst, most crime-ridden areas of the city and turning the area into a giant open-air prison.
Bruce Wayne is concerned enough about the situation to take a public stand against it but is arrested and dumped into the new Arkham by Hugo Strange, who succeeded Quincy Sharp as warden/administrator. Bruce gets in touch with Alfred, the Batwing makes a flyby, and Batman takes wing into a seething environment of chaos and destruction.
Harley Quinn has taken a medical team hostage in Gotham Cathedral, Harvey Dent (Two-Face) is preparing to dip Catwoman in acid, hungry, desperate prisoners roam the streets, and Hugo Strange's voice booms over the city's PA system announcing that "Protocol 10 will commence in 10 hours."