A young girl (Phyllis Thaxter) from a good family in a small town is engaged to a charming young man (Henry H. Daniels Jr.). But no one knows she is mentally ill. She has another darker personality living inside her and who is trying to take dominance over her body ... even if she has to kill to do it. Based on a radio play ALTER EGO by Arch Obler (FIVE), who also directed the film. A fascinating curio to have come out of 1940s MGM. It's a precursor to films like THREE FACES OF EVE and SYBIL. It shows how little the medical establishment and society knew about split personalities at that time. No reason is given for the dual personality but it suggests that sexual repression might have something to do with it. When she kisses a man (Stephen McNally), she is frightened of the passion she feels while her "other" loves it. Thaxter in a rare leading role is very good but I might have been more impressed if she provided the voice of the evil "other" which is done by Audrey Totter. There's a nice score by Bronislau Kaper which elevates the film. With Edmund Gwenn as the psychiatrist who first discovers the dual personality, Addison Richards and Kathleen Lockhart.