The film begins amidst the peaceful backdrop of a forest, where Vivian (Hadley Robinson), a 16-year-old girl, is seen running alone, suddenly stopping to let out a quiet scream. She soon finds herself waking from a daydream to her mother, Lisa (played by Amy Poehler), who is eagerly preparing to capture their yearly first-day-of-school photograph. This time, however, Vivian feels she's grown out of this tradition and chooses instead to take a spontaneous picture of her mother, embracing the changes in her life.
As she steps into Rockport High School, Vivian reconnects with her close friend Claudia (Lauren Tsai), who is obsessively focused on an upcoming list of superlatives. Their day begins in Mr. Davies' (Ike Barinholtz) classroom, where announcements reveal that the charming Seth (Nico Hiraga), has returned after a significant transformation over the summer, attracting newfound admiration.
During class, the entrance of the insightful newcomer, Lucy (Alycia Pascual-Peña), ignites a debate when she critiques F. Scott Fitzgerald's "The Great Gatsby," claiming it reflects mere entitlement. This comment prompts Mitchell (Patrick Schwarzenegger), the star athlete, to defend the literary classic.
Later, a trip to the supermarket places Vivian and Lisa face-to-face with John (Clark Gregg), a flirtatious coworker of Lisa's, who is met with indifference. As the school year progresses, Claudia notices Vivian's interest in Seth, while Lucy confronts Mitchell over his rude behavior, leading to a tension-filled interaction that culminates in Lucy's declaration that everyone deserves respect.
Amidst the unfolding drama, Principal Shelly (Marcia Gay Harden) is drawn into the conflict when Lucy reports Mitchell's actions, prompting discussions on fairness. As Vivian strives to create a meaningful college essay, she seeks inspiration from Lisa's experiences as a feminist pioneer. Through heartfelt conversations and sharing music from Bikini Kill, Vivian becomes deeply inspired, fueled by Lisa's collection of "zines" that resonate with her passion for empowerment.
The chaos intensifies at the pep rally as the jocks’ superlative list stirs humiliation among the girls; Kaitlynn (Sabrina Haskett) breaks down upon being labeled "Best Rack," while Emma (Josephine Langford), the head cheerleader, is dubbed "Most Bangable." Vivian herself is tagged as "Most Obedient," a title that ignites her frustration.
In response to the clamor, Vivian decides to create her own 'zine, titled "Moxie," stirring swift reactions as girls gather in school bathrooms, energized by its empowering message. However, backlash soon follows from Mitchell and Jason (Joshua Walker), who wrongly assume Lucy is behind the project and retaliate against her.
As excitement brews, Vivian's movement gains momentum with the support of Lucy, and Seth gets involved by promoting Moxie posters in the boys’ restroom. A protest against the oppressive dress code is crafted, but complications arise when Claudia's mother insists on a more conservative outfit.
With the homecoming game approaching, controversy erupts when Mitchell gets nominated for an athlete scholarship, igniting outrage that prompts Kiera, an athletic peer, to assert her own candidacy. Battling frustrations among her friends, Vivian finds comfort in her blossoming relationship with Seth, sharing a sweet moment that culminates in a kiss after some humorous mishaps.
As the Moxie campaign heats up, Vivian leads a spirited meeting within the locker room, igniting enthusiasm among girls, with Emma initially intrigued but soon retracting her interest. Despite Mitchell's counteractions and attempts to downplay the girls’ efforts, Vivian's movement becomes a beacon of hope.
During a chilling encounter at school, Vivian discovers a heartbreaking note from a fellow student who has suffered a traumatic experience, leading to an outburst that compels her to spray-paint "RAPEPORT" on the school's steps as a powerful statement. This act of rebellion, along with a rallying call via Moxie's Instagram page, sets the stage for a dramatic school uprising.
As Mr. Davies reads Shelly’s reprimand aloud, a surprising wave of support washes over the students, culminating in Vivian's empowering address that galvanizes the crowd. Emma takes the opportunity to share her painful story about Mitchell, garnering overwhelming empathy and solidarity from classmates.
By the story's conclusion, Vivian, alongside her friends, realizes the strength in unity and resilience as they gather for a jubilant celebration, marking a significant victory for Moxie and highlighting the transformative power of collective action against systemic injustices.
