Dan Gallagher, a popular high school jock, enjoys a seemingly perfect life with his girlfriend Beth. During a spring break, he engages in a passionate weekend affair with Alex Forrest, an intelligent and alluring teenage girl he meets at a high school mixer. When Dan attempts to end the liaison and return to his girlfriend, Alex refuses to accept rejection. What begins as persistent phone calls and chance encounters escalates into a terrifying campaign of psychological and physical terror. Alex insinuates herself into Dan's life, befriending his girlfriend and destroying everything he holds dear. As the obsession intensifies, Dan finds himself trapped in a nightmare of his own making, unable to convince anyone of the danger Alex poses. The film becomes a cat-and-mouse game where Dan must protect his girlfriend from a girl whose love has transformed into murderous rage, exploring themes of infidelity, obsession, and the devastating consequences of casual cruelty.
