Ben Cronin is a high-school jock who once had a drug problem. An aspiring Olympian, Ben is training to impress a visiting athletic scout from Stanford University. Ben is dating a girl named Amy Miller and works with his mother at the local hospital. A new girl named Madison Bell transfers to Ben's school and immediately begins to seduce him, eventually convincing him to have sex with her in a pool. Ben considers the event a one-night stand, but Madison insists that the two continue to be together. Ben, after reflection, finally rejects her in favor of his girlfriend. The possessive Madison becomes obsessed with Ben and turns his life into a living hell as she stalks him, even managing to become friendly with Amy and Ben's mother. After Ben conclusively tells Madison that he wants nothing to do with her because he is with Amy, the "horror" truly begins as Madison reveals that she has a violent streak and will never let him go – even in the face of death.