Nineteen-year-old Beth recounts to a court-appointed psychiatrist the events leading to the disappearance of her 7-year-old sister. Denny, an ugly child born to Beth's beautiful and ambitious parents, is kept hidden at home, for she is also believed to be mute and mentally deficient. To Beth, Denny demonstrates uncanny abilities, and Beth is about to announce them when her little sister begins to act out in vengeance against those who reject her. When the man Beth has fallen in love with becomes one of Denny's targets, Beth's loyalty to her sister waivers. She needs to escape Denny, to be rid...