Kenneth (William Hopper) and Christine Penmark (Nancy Kelly) love their eight-year-old daughter Rhoda (Patty McCormack). Rhoda appears to a normal child but she is anything but. Kenneth is in the military and goes away on assignment. When neighbour Monica (Evelyn Varden) comes over with gifts for Rhoda, Rhoda tells her about how she lost a penmanship medal to another kid in class. Monica laughs off the lose but Rhoda is clearly furious about it.
Later Christine and Monica are having lunch when they hear a child drowned at school picnic. Fearing it might be Rhoda Christine races to the scene to find the Rhoda is fine. The victim turns out to be the boy who won the penmanship medal. Later Rhoda’s teacher comes over to talk to Christine about Rhoda. The teacher says that Rhoda was the last person seen with the boy and his medal is missing. The boys parents come over demanding to talk to Rhoda to find out what happened. Christine sends everyone away. The teacher tells Christine that Rhoda isn’t welcome back to school.
Christine starts to investigate and finds out the Rhoda has the missing medal. She claims that the boy gave it to her. Christine talks to her father and finds out that she was adopted and that she is the daughter of serial killer. Christine worries that Rhoda is a killer too and because of genetics.
Later Christine catches Rhoda trying to burn her tap shoes which she realizes Rhoda used to beat the boy before he drowned. A caretaker bugs Rhoda about the boy’s death and then he “mysterious” dies horribly. Christine is torn on what to do.
This 1956 horror movie was based on a play of the same name where the ending was quite different than the movie. Because of the production code criminals couldn’t get away with crime so the ending was changed for the film. Nancy Kelly, Patty McCormack, Eileen Heckart and Henry Jones all starred in the original play and reprised their roles for the movie.