Harleen is the prequel installment of the Harley Quinn film series. taking place before Harley meets the Joker.
A Film begins in Brooklyn elementary, a girl named Harleen Quinzel is bullied by Copperhead and her friends. She's been injured and beaten to death, one of the school staff's rather talking on the phone instead of helping her. Harleen's twin, Lauren told her that there's nothing to be afraid of and volunteer to be her but Harleen refuse her offer.
In the girls bathroom, Harleen and Lauren are hiding in the stall during lunch, Copperhead's trying to find Harleen but Lauren steals her identity as Harleen which Copperhead tells everyone about her accident. Harleen accidentally clogged the toilet with the toilet paper and escape from the school, where she gets hit by a bus and lapsed into a coma.
In her dreams, Harleen saw some of her memories where she pooped her pants thanks to Lauren, She discovers that Lauren is such a snitch. Harleen blamed her twin and vow to destroy her.
A few months later, Harleen wakes up and her mother told her that Lauren becomes friends with Copperhead, Harleen looks at the mirror which sees that her face is white and hair is red and black shocked. Her mother then leaves and when she does Harleen breaks everything she can before acting more like Harley Quinn to sneak revenge.
At the town, Harley's looking at Lauren and Copperhead's friend's plotting for something, so she end up steal the blueprints. Harley discovered that it's a plan for some sort of a domination around the coney island and manage to prevent them.
Harley saw a school staff who's talking on the phone and manage to sneak revenge on her first for not helping her. The school staff reveals that she can tell Harley exactly where Lauren is. She's at the docks preparing for the Coney Island's Domination in tomorrow. Harley beats her with a baseball bat before running off.
The next day, Harleen wakes up and doesn't remember anything. She discovers from her mirror that she has another personality.