The story unfolds with PJ (Rachel Sennott) and Josie (Ayo Edebiri), two high school seniors eager to fulfill their pre-graduation fantasies, gearing up for a night that promises potential romance. Their eyes are set on two cheerleaders: the charming Brittany (Kaia Gerber) and Isabel (Havana Rose Liu), who is unfortunately already involved with the prominent quarterback, Jeff (Nicholas Galitzine).
As they head to the local carnival, where fellow students from Rockbridge Falls High are gathered, PJ and Josie nervously approach their crushes, only to be met with awkward silences. An unexpected encounter occurs when Hazel Callahan (Ruby Cruz) mistakenly assumes they are former delinquents, leading them to quickly rectify her misconception.
As the night progresses, they learn of Isabel’s strained relationship with Jeff, triggered by his disloyalty. In a bid to help Isabel, Josie offers her a ride home, although they soon find themselves confronting Jeff, who tries to interfere. Encouraged by PJ, Josie takes the decisive step to send Jeff crashing to the ground, prompting an exaggerated reaction from his football peers. With that, they make a hasty escape, leaving a whirlwind of chaos behind.
Throughout the school year, PJ and Josie's unease grows as they fear retaliation from Jeff and his friends, who seem determined to make their lives unbearable. When summoned to the office of Principal Meyers (Wayne Pére), the girls devise a clever ruse, claiming they had undergone self-defense training to promote female solidarity, which miraculously convinces him to let them off the hook.
In a rare moment of downtime, the girls engage in deep conversation with Hazel, which ignites a compelling idea: the formation of a "fight club." Although Josie is hesitant, PJ pushes forward, revealing that their true intention is to attract Brittany and Isabel by promising them opportunities for deeper connections. With Hazel's support, they begin recruiting other girls, fabricating tales of their supposed time in juvenile detention to bolster their credibility. The situation escalates when Josie, during a training session, lands a punch on PJ, resulting in a bloodied nose and a heated moment of confrontation.
They seek counsel from Mr. G (Marshawn Lynch), who is struggling with his own personal issues but ultimately agrees to mentor them. The first official meeting of the club sees both Brittany and Isabel in attendance, leading to PJ's desperate attempt to salvage the situation by matching Josie against Annie ([Zamani Wilder]). Mr. G steps in, sensing the deteriorating circumstances.
As sessions progress, club members learn to channel their budding fighting talents while bonding over shared experiences that elevate the tension amongst them. In an emotional circle, they share deeply personal stories, including Josie's fictional account of juvie, which unknowingly impacts Isabel.
Meanwhile, Tim ([Miles Fowler]), a friend of Jeff, grows suspicious and tries to instill fear in the girls to disband the club. Hazel’s mother, Mrs. Callahan (Dagmara Dominczyk), begins to notice her daughter's newfound activist spirit but remains oblivious to Hazel's deeper secrets. One day, Hazel stumbles upon the shocking truth — her mother is involved with none other than Jeff.
As Hazel expresses her shock to PJ and Josie, the bond among the trio begins to fray. Josie, feeling a connection to Isabel, divulges this scandalous information to her, intensifying their relationship. However, Hazel eventually confronts Jeff, demanding an explanation for his infidelity. In a moment of fierce indignation, she rejects him, declaring her need for justice.
Under the cover of darkness, the girls enact a plan to seek revenge on Jeff, launching eggs and toilet paper at his house. While they wait for the responses, Josie and Isabel share a heartfelt conversation in their van, further deepening their growing connection. However, Hazel uses this chaotic moment to set a bomb under Jeff's car, leading to a cataclysmic explosion that sends everyone scampering just as Josie and Isabel were about to share their first kiss.
In the aftermath of the explosion, a tense meeting unfolds where PJ critiques Hazel's reckless decision to retaliate. This incites a confrontation, resulting in emotional upheaval, and PJ crosses a line by insulting Hazel's mother, leaving her devastated. Meanwhile, Josie and Isabel navigate their developing relationship amidst the chaos. PJ also seeks connection with Brittany but receives a rejection that forces her to reconsider the nature of their bond.
The dynamics at school shift dramatically as Jeff and Tim confront the Fight Club, ready to expose their deception about juvenile detention. They coerce Hazel into facing Tucker ([Cameron Stout]), leading to a showdown where Hazel faces defeat despite her bravery. Just as the truth about PJ and Josie's motives surfaces, the club is thrown into disarray, and their deception unravels.
As Josie reflects on the events, she gains insight from Rhodes ([Punkie Johnson]), a past student, prompting her to reevaluate her priorities. With newfound determination, she teams up with PJ to fight back against the cruel pranks directed at their football team, gathering other girls for support.
On the day of a critical football game, PJ and Josie lead a daring mission to protect their team. With Hazel and new allies, they devise a plan that falters initially when a bomb fails to detonate as expected. They pivot to create distractions, leading PJ to kiss Ella ([Summer Joy Campbell]) to captivate the players' attention long enough for Hazel to use her knowledge of Jeff's pineapple allergy to their advantage.
As they collaborate, their strategy pays off, successfully pulling Jeff out of harm's way just as the opposing team arrives. The skirmish escalates into an intense clash, showcasing the girls' newfound physical prowess. In the end, the girls emerge victorious, celebrated by their peers as their bonds with each other strengthen. Josie and Isabel share a passionate kiss while PJ and Hazel savor newfound mutual attraction—just as Hazel's earlier sabotage plan finishes with a dramatic explosion, encapsulating the tumultuous adventures they've navigated together.
