The story tells of a young woman admitting to having blackouts, fearing they are getting worse. She is diagnosed as suffering from multiple personalities, as a result of severe abuse at the hands of her mother, whom her psychiatrist, Cornelia Wilbur, believes was schizophrenic. The movie Sibyl is based upon author Flora Rheta Schreiber's biography of Shirley Ardell Mason, an American psychiatric patient, suffering from multiple personality disorder. The book, also called Sibyl, was in its turn based largely on the actual accounts of psychiatric treatment that Shirley Ardell Mason underwent, documented by American psychiatrist Cornelia Wilbur