Ann Lake (Carol Lynley) is a young mother who arrives at her daughter's preschool to collect her after her first day, only to discover that nobody has ever seen the four-year-old child, despite Ann claiming she exists. Superintendent Newhouse (Laurence Olivier) becomes involved in the case and begins to suspect that Bunny Lake may not be a real person. As Ann's anxiety and desperation grow, so does the tension, leading to a suspenseful and disturbing climax as Steven, Ann's brother, is revealed to be the perpetrator. The film follows a complex web of psychological manipulation, family secrets, and emotional manipulation that keeps the viewer on edge until its shocking conclusion.