Batman is incarcerated in Arkham Asylum after being exposed to the Scarecrow's fear-inducing gas. Batman knows that the Scarecrow has escaped for the second time and is planning to poison Gotham's water supply with the same fear-inducing gas. Can Batman bring himself to break the law and escape from Arkham before the Scarecrow brings Gotham to its knees?

Batman must stop Roland Daggett's plan to release a viral plague designed by Professor Milo into Gotham by way of its stray cat population. The case gains new urgency when Catwoman becomes infected with the virus during her search for her missing cat, Isis. Now, Batman must find an antidote to save the woman who loves him most.