Killer Croc is under the Black Mask's mind control. He's sent to The Hill in Gotham to carve out some space so that The Black Mask can move in and take over. That means a confrontation with Onyx. She loses four of her crew in their first confrontation and is lucky to escape herself. Seeing that she may be out of her depth, she seeks the help of Catwoman. If The Hill falls to the Black Mask, that would leave only the East End for him to conquer.