When Ann Lake (Carol Lynley) comes to a nursery school in the Hampstead area of London to collect her four-year-old daughter, Bunny, she's told by everyone from the headmistress down that there is no record of the child having been at the school. Ann's brother, Steven (Kier Dullea) an American journalist, tries to help solve the mystery. And after Investigator Newhouse of Scotland Yard is unable to find evidence of Bunny ever being enrolled, he hints that the child could be a figment of the young unmarried mother's imagination. Ann desperately insists that her Bunny is both real and missing. While searching for something that might give the authorities proof of Bunny's reality, Ann finds that the child's toys and possessions -- even her passport -- are all missing. Remembering a doll she sent to a "doll's hospital" for repair, Ann rushes to claim it. And after it helps uncover a well-planned plot to make her doubt her sanity, Ann is able to find herself when they finally find her missing daughter.