After splitting with the Joker, Harley Quinn joins superheroes Black Canary, Huntress and Renee Montoya to save a young girl from an evil crime lord, Black Mask in Gotham City.After the events of Suicide Squad, Harley Quinn has left the Joker. When a young girl named Cassandra Cain comes across a diamond belonging to a crime lord by the name of Black Mask, Harley joins forces with Black Canary, Huntress and Renee Montoya to protect her