WARNING: The following contains spoilers for Batman: White Knight Presents Harley Quinn #4, by Katana Collins, Sean Murphy, Matteo Scalera, Dave Stewart, and AndWorld Design, on sale now.
Batman: White Knight Presents Harley Quinn has done well to hide the identity of its mysterious killer, Starlet. Everyone from FBI agent Hector Quimby to Neo Joker has been pegged as a a suspect, with the latter perhaps creating a new identity and disguise that even fooled Harley Quinn.
However, in Batman: White Knight Presents Harley Quinn #4, the curtain drops on this serial killer, and it's someone close to Hector with a tragic, sympathetic past.
Harley's been struggling mentally as she doesn't know if she can make amends for the trouble she, Joker, and Batman caused Gotham in the past. Bruce gives her a pep talk in prison, however, and she returns home, guns blazing as she wants to crack the new case. She garners clues and arrives at an old theater, where ironically Hector and Duke are trying to break in. They're all being played, obviously, but they're taking the bait as they need more info.
But it goes all wrong on the inside with Duke running off and getting knocked out by Starlet's boss, the Producer. It turns out he's creating a new network of criminals, a renaissance as he calls it, and he wants Starlet to be his leading lady. He even threatens her if she goes off-script but it does appear she's back on track as she ties Harley down to a projector and then drops the trump card on a nervous Hector.
As an old film from his childhood plays, we see five-year-old Hector being abused by his mom, Sofia Valentine, with Ethel, his nanny, trying to shield him. Sofia's angry her career is going down the drain and blames him, with Ethel indicating he's a loving child who doesn't deserve this. Sofia insults her and smashes a bottle in her face, which would require multiple surgeries and end her aspiring acting career. This drove Ethel crazy and Hector's stunned to find out she's now seeking revenge as Starlet.
Ethel even wants him to be the Bonnie to her Clyde, admitting she murdered all the other actresses because they were just like Sofia -- women who spat on the concept of motherhood and abandoned kids to prolong their career. Hector's in two minds as he feels sorry but knows Starlet killed many people to set him down this path. Still, Ethel's always had a hold on him, not just as a nanny, but as the perfect mother, which is why he decides to train his gun on Harley. He's always been an outsider and like Ethel, he feels accepted in this theater and is now ready to follow his new mentor down the dark side.