Batman: Arkham Trilogy(Arkham Knight)Walkthrough Part 4 

Nine months after the Joker's death, crime rates in Gotham City have dramatically declined, but Batman anticipates a new threat and maintains a vigil over the city. Before his death, the Joker sent his mutated blood to Gotham's hospitals, and several patients were infected. While most were cured, the patients who were not treated are starting to look and act like the Joker. Batman researches a cure for the mutations, and orders Robin to watch over the infected.