The 17-year-old twin sisters Abby and Lily, on the last day of school, go with their friends to celebrate graduation at an abandoned warehouse. The sisters quarrel, and Lily leaves the party. Rick Hansen, an English teacher at the school, who was following Abby in his car, offers to drive Lily home and soon sedates her with the help of chloroform. As the family copes with the girl's disappearance, the police begin a search. Lily wakes up in Rick's locked basement.