Her parents being zoologists, Cady Heron has never known what "high school" truly meant. She lived her first 15 years in the African jungle, home-schooled, living life with only her parents and the animals of the wilderness, knowing all of the rules of survival. However, when she moves out of Africa, she has to learn the rules of high school, a jungle in itself. She instantly makes friends with two sweet teenagers, Damian and Janis, who, in the terms of the high school, were in the "out crowd." Soon she meets the Plastics, the three crude, beautiful, popular girls, consisting of Regina, the unofficial leader, Gretchen, Regina's full-time follower, and Karen, "one of the dumbest people you will ever meet." They immediately let her into their group, but Cady, wanting to keep her first friends, is unsure. The two convince Cady to keep her relationship with the Plastics, only so that they can know their dark secrets. However, events turn for the worse when Cady falls for Regina's ex-boyfriend, Aaron Samuels. When Regina finds out, she seeks revenge of Cady by taking Aaron back. When Cady finds out, what began as a game to discover secrets turns into a plan to destroy Regina. Now, Cady, Janis, and Damian plot together to bring Regina's status down. However, as Cady spends more time with the Plastics, she, too, begins to become one.