When high school student Cassie Stoddart is found fatally stabbed in a house on the outskirts of Pocatello, Idaho, the community is gripped by fear that a random killer is on the loose. The police reconstruct Cassie's last hours and focus on three classmates who were the last people to see her alive. As the investigation narrows, detectives uncover a shocking buried videotape that reinterprets the case, raising the unimaginable question of whether the 16-year-olds could have committed such a brutal crime.