In order to infiltrate the Secret Society, the Justice League of America has come up with a plan to have Catwoman caught by them in the act of trying to steal a Martian artifact and incarcerated in Arkham Asylum. As Catwoman is the only member of the team who is not publicly known to be a member of the team, she is their best shot as a mole.
After she is locked away, Catwoman is introduced to Dr. Jeremiah Arkham. He believes that she has a dual personality syndrome which requires her to wear the costume, and invites her to become part of his Operation Avatar, to cure her. Refusing to be medicated or "fixed", she kicks away his tray of medication. After restraining her again, Arkham changes his tone, warning that he can keep her there forever. He has her transferred to the Super-Max wing - where the hardcore psychos go.
She is placed in a cell between Black Mask and Vortex, who - after the guards have gone - give her clues as to how to escape. Thanks to her diamond-cutting claws, she escapes her cell, and Vortex's ability to repel matter gets him out as well. He creates the diversion she needs to get out - except with far more destruction than she expected. His tremors threaten to bring down the whole asylum. Even so, she manages to escape the guards while they chase him, and sneaks up on Jeremiah Arkham in his control room. She wraps him in a straight-jacket. Still, as she drags him around as hostage, he begins trying to psychoanalyze her, and it grows annoying to the point that she simply knocks him unconscious.
Finding a crow statue that Black Mask pointed her to, she pokes in its eyes, and it activates a secret floor panel revealing a way down. She finds herself in a vast tunnel, adorned with decorations and stairways. This is the Gotham Underground. She begins to hear people coming toward her, and rather than meet them, she climbs the dead vines spiralling everywhere to a the source of a glint of light that she spots on a wall. Finding her way to the surface at last, she is worried to see that there is a massive police presence right in front of her.