Gotham City crumbles after the Joker’s public breakup with Harley Quinn. When a young girl named Cassandra Cain comes into possession of a valuable diamond belonging to Black Mask, a ruthless crime lord, Harley finds herself targeted by various factions of Gotham’s underworld, all seeking the girl and the gem. Forced to rely on her wit, agility, and a ragtag team of female vigilantes including Huntress, Black Canary, and Renee Montoya, Harley must protect Cassandra and face the madness that awaits them.