After the death of her husband, high school teacher Amanda moves back to suburban Texas from Guadalajara, Mexico, having adopted her seven-year-old stepson, Rodrigo. The film opens as Amanda and Rodrigo discover a disemboweled cat behind their house. Soon, more mutilated pets begin to appear around the neighborhood. Amanda, impelled by Rodrigo's increasingly violent behavior in school and the suspicions of the other teachers, begins to suspect that he's behind the killings, a result of the emotional disturbance of losing his father and leaving home. Rodrigo, however, has a different theory about the culprit-the chupacabra, a monster of Mexican legend.