After the Joker assaults Gotham City Hall, he is apprehended by Batman and escorted to Arkham Asylum; the asylum also temporarily holds many members of Joker's gang, displaced by a fire at Blackgate Prison.Believing Joker allowed himself to be captured, Batman accompanies him into the asylum. Joker's plan is revealed, as Harley Quinn takes control of the building's security and Joker manages to escape his captors, aided by a corrupt asylum guard who kidnaps commissioner Gordon. Joker threatens to detonate bombs hidden around Gotham City if anyone attempts to enter Arkham, forcing Batman to work alone.While pursuing Quinn to rescue Gordon, Batman is exposed to the Scarecrow's fear toxin, hallucinating the talking corpses of his parents, and Gordon's death. Batman fights off Scarecrow and the toxin's influence, and eventually navigates his way to a secret Batcave installation he had hidden on the island, restocking his gadgets.

Batman finds Quinn and knocks her unconscious before rescuing Gordon; Joker then directs Batman to the captured Bane who has been experimented on by asylum doctor Penelope Young. After freeing and subsequently fighting an enraged Bane, Batman learns that Joker has returned to the asylum to gain access to Young, who has been developing Titan, a significantly more powerful version of the Venom drug that grants Bane his strength, intending to use it to help patients survive more strenuous therapies; Young refused to hand over the Titan upon learning she was working for Joker, who plans to use the Titan to create an army of superhuman henchmen. While searching for Young, Batman is again attacked by Scarecrow and the fear toxin, hallucinating the deaths of his parents. After he recovers, Batman destroys Young's Titan formula and rescues Young from the clutches of Victor Zsasz, but she is then killed by a rigged explosion; the Joker obtains the already completed batches of Titan. less