WARNING: The following contains spoilers for Batman: White Knight Presents Harley Quinn #1 from Katana Collins, Sean Murphy, Matteo Scalera, Dave Stewart, and AndWorld Design, on sale now.
Batman: White Knight focused a lot on Harley Quinn trying to keep Jack Napier sane, ensuring his Joker couldn't return to undo the good work he was doing for Gotham City. He played the political angle that every running mayor would, while even getting the Batman to question his role and how effective his war on crime was.
Still, the Joker came back but would be suppressed by the time it was over, only to emerge once more in Curse of the White Knight. While Jack was eventually killed by Harley, but Batman: White Knight Presents Harley Quinn #1 resurrects one of the franchise's deadliest clowns in the form of the Neo-Joker who wants to carry on his bloody legacy.
The Neo-Joker, aka Marian Drews, was a suicidal bank teller Joker took hostage. Given her looks and the fact Harley left him, the sadistic clown mistook her for Harley, a role she fell into easily as she loved him. When he proposed, Marian realized he had no clue she was the second version of the jester. She grew angry and was eventually beaten up when the real Harley returned and threw her to the wayside. As the story progressed, Marian would return as the Neo-Joker, angry Jack put his evil persona to bed. She'd co-opt a freeze gun from Mr. Freeze and use Clayface to mind-control most of the city's villains, waging war on Gotham, the Bat-family, and Harley. She aimed to hurt Jack by bringing the clown back and while she succeeded, Harley once more beat her down and got her locked up, which is why it's shocking Marian's back.
In this spinoff, Harley's struggling with her new role as mother to two hyenas as well as Joker's twins. She doesn't know if she has the mental fortitude for motherhood, much less to take on the case that Duke Thomas brings to her called the Golden Age Murders. A bunch of movie stars are being killed and Harley eventually goes to Bruce -- imprisoned after Curse -- and he convinces her she's strong enough to use her talent as a criminal psychologist and profiler to help the FBI. When she visits the crime scene of James Turner, she realizes the tools being used, the style, and the clues left behind are from a Joker copycat.
She dons her old costume and steps out as it's personal as she doesn't want Marian sullying Jack's name. It remains to be seen how Marian escaped and who she's working with, but Harley knows she'll have to revert to her aggressive ways to deal with a psychopath that's not afraid to kill to prove she's Joker's successor and who seems to be angry he's gone.