Cady Heron, a 16-year-old girl who has spent her entire life being homeschooled in Africa, moves to the United States and enrolls in a public high school for the first time. This transition introduces her to the complex social hierarchies and cliques that define high school life. She initially struggles to find her place, befriending social outcasts Janis and Damian, who guide her through the school's social landscape. Together, they concoct a plan to infiltrate the school's most exclusive and ruthless clique, The Plastics, led by the charming yet manipulative Regina George.

As Cady becomes more integrated into the group, her initial intentions begin to fade, and she starts to absorb the group's superficial values and backstabbing behavior. Her newfound popularity strains her relationships with Janis and Damian, and she slowly starts to lose sight of her true self. The dynamics within The Plastics and the broader school community lead to escalating tensions, prompting Cady to reevaluate her priorities and the consequences of her actions.