After the Joker assaults Gotham City Hall, he is caught by Batman and taken to Arkham Asylum, which temporarily houses many members of the Joker's gang, who were transferred after a fire at Blackgate Prison. Believing the Joker allowed himself to be captured, Batman accompanies him into the asylum. The Joker's plan is revealed as Harley Quinn takes control of the security and the Joker escapes into the facility, aided by a corrupt guard who kidnaps Commissioner Gordon. The Joker threatens to detonate bombs hidden around Gotham City if anyone tries to enter Arkham, forcing Batman to work alone.
