Harley Quinn broke up with Joker, and after a while she told Gotham about it by blowing up that very chemical plant. The woman no longer mourns the failed relationship; she has no time for it, as she has also lost her inviolability, and now she is being hunted by criminals of varying degrees of criminality who want revenge. And by that time, the Gotham godfather Roman Sionis is eager to recover the missing diamond, which was stolen from his henchman by a juvenile pickpocket.