The storyline picks up with Harley Quinn (Margot Robbie) just following her dastardly dreamboat, The Joker, breaking up with her, with the spinout of their toxic relationship leaving her in shambles. An oft-unhinged club owner named Roman Sionis (Ewan McGregor), whose alter ego is another powerful villain in Gotham City known as Black Mask has secured a rare diamond worth so much that he could afford to up his protection racket operation to become the biggest crime kingpin in Gotham City. That diamond is stumbled onto and taken by a pickpocket extraordinaire named Cassandra Cain, who ends up swallowing it to avoid having to give it up when frisked by police, making her the most sought after person in the city, especially after Roman places a half-million-dollar bounty on her.
All of this leads to Harley forming a ramshackle team of women with grievances with Black Mask to finally put an end to his murderous ways. That team includes Huntress, aka Helena Bertinelli (Mary Elizabeth Winstead), a Punisher-type mafia princess-turned-vigilante who rides a motorcycle and shoots a crossbow – Black Canary, aka Dinah Lance (Jurnee Smollett-Bell). Leading the case for the Gotham City Police Department is Renee Montoya, played by Rosie Perez, and newcomer Ella Jay Basco portrays Cassandra Cain. Cathy Yan directs.