Rhoda Penmark (Patty McCormack) has the adults in her life completely fooled, but when her uncontrolled hellishness leads her to murder schoolmate Claude Daigle in order to steal a penmanship medal which she wanted – and set on fire the weird, child-like handyman Le Roy (Henry Jones) who taunts Rhoda with accusations about the murder – her mother Christine (Nancy Kelly) becomes tragically aware.
Christine learns from her own father (Paul Fix) that she herself was adopted and her real mother was a conscienceless serial killer and realises that Rhoda is a ‘bad seed’ – a genetically malignant person.
But who would believe her – Rhoda is the perfect angel in the eyes of everyone she meets.
Also in the cast are 1950s sci-fi star William Hopper as the loving husband away in Washington for most of the film; Evelyn Varden as Monica, the friendly, aunt-like apartment owner; and a scene-stealing Eileen Heckart as the distraught, alcoholic mother of the dead boy.
A 1985 ABC TV remake starred Carrie Welles, David Carradine, Lynn Redgrave and Richard Kiley.