Josie Geller, played by Drew Barrymore, is an exceptionally bright but socially awkward copy-editor working for the Chicago Sun-Times. Despite her intelligence, she feels stuck in her role and yearns to become a reporter. Her boss, Gus, takes note of her enthusiasm but doubts her capability for the job. This causes Josie to feel increasingly discontented with her life, leading her to withdraw from others, perplexing her promiscuous co-worker, Anita.
In a surprising turn of events, during a staff meeting led by the domineering editor-in-chief, Rigfort, Josie is assigned an undercover reporting task at a local high school to help parents gain a better understanding of their children's experiences. Although thrilled by the opportunity, both Anita and Gus express their concerns about this risky venture, fearing it may end in disaster. However, Josie is determined and rushes to inform her brother, Rob, who works at a postage store called the Tiki Post. Rob, a once-popular high school baseball star, warns her against the idea and reminisces about her own traumatic high school days when she was cruelly dubbed "Josie Grossie." This nickname still haunts her, contributing to her absent romantic experiences.
On her first day at South Glen South High, Josie's enthusiasm quickly turns into despair as she reverts to her old, awkward persona. She arrives late to class, suffers an unusual punishment involving a sombrero from her quirky teacher, and has an unfortunate encounter with the "mean girls" of the school, including Guy Perkins, the charmingly popular student. However, hope emerges when she befriends Aldys, a sweet and intelligent girl who refers to Guy and his friends as "lemmings." Aldys encourages her to join a group of academically inclined students, but Josie's tactics to get the scoop fail.
As time goes on, Josie develops a crush on her appealing young English teacher, Sam Coulson, who shares her passion for Shakespeare. After an embarrassing mishap recalls memories of being ridiculed in high school, Josie’s life takes another twist when her past crush, Billy Prince, invites her to the senior prom, rekindling her long-lost dreams. However, her newfound confidence faces a challenge when Josie's undercover assignment takes a complicated turn.
With Gus growing impatient over Josie's lack of story development, he instructs her to integrate with the cool kids, equipping her with a hidden camera to report back. As Josie's secret life escalates, Anita finds herself drawn to Gus, creating romantic tension amid the workplace antics.
Josie's journey takes an emotional toll as she reveals her vulnerability to Rob, revealing her deep-seated fears of rejection and the persistent echoes of high school trauma. In an effort to reinvent herself, she pursues popularity but soon realizes the cost of such a transformation. After a series of humiliating events, Josie confronts her peers and herself, making a powerful statement about authenticity over popularity.
As prom night arrives, Josie’s choices lead to an unexpected climax where she is voted prom queen, yet her moment of glory quickly spirals into chaos when her past resurfaces. She bravely confronts the shallow nature of her high school tormentors, asserting the importance of being true to oneself, even if it means stepping away from acceptance.
Finally, Josie focuses on reclaiming her narrative by writing a compelling piece about her experiences, emphasizing the challenges faced by students in high school. In a heartwarming conclusion, she courageously stands in a baseball field, waiting for Sam to find her. As time ticks away and hope wanes, Sam unexpectedly arrives just in time, offering the most anticipated kiss that solidifies her journey from obscurity to acceptance.
