Killer Croc rolls into the East End tearing up anyone dumb enough to get in a croc/human's way! And where Croc goes, can Onyx be far behind? Confused? So's Catwoman, but she hardly has time to ask questions!
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.