Josie Geller is an insecure copy editor for the Chicago Sun-Times who has never experienced true romance. She gets her first reporting assignment to go undercover as a high school student and report on today's adolescents. At 25 years old, Josie eagerly but anxiously steps back into high school, where her traumatic memories of being a nerd resurface. Recreating herself as "Josie Grossie," she befriends Aldys, a sweet and intelligent girl, becoming part of the mathletes. However, her attempts to fit in with the popular crowd, led by Guy Perkins, often lead to embarrassing and uncomfortable situations.

As Josie navigates the treacherous waters of high school life, she develops a crush on her English teacher, Sam Coulson, who inspires her with his passion for literature. Her brother, Rob, a former high school baseball star, joins her undercover mission to help her gain popularity and gather more insights. Through her journey, Josie juggles writing the article, maintaining her cover, and dealing with her resurfaced high school feelings. Along the way, she learns significant lessons about self-acceptance, the pressures of adolescence, and the importance of being true to oneself.