There must have been something of a fad for female twin movies in 1946. The Bette Davis vehicle A Stolen Life was released and Olivia de Havilland made dual appearances her own twin film. The Dark Mirror follows the good twin/evil twin paradigm, with the evil twin trying to drive the good one out of her mind. The story has the great potential for a tense film noir, but unfortunately the tone often dissipates any tension before it is able to build.
The film opens with shots of a murder scene in a New York penthouse apartment. The resourceful Lieutenant Stevenson (Thomas Mitchell) learns it is a doctor that has been killed and begins interviewing other tenants in the building and they lead him to a young woman who works at the magazine stand in the lobby of the medical building. She was spotted by several witnesses leaving the crime scene, but she has an alibi, having gone to a concert in Central Park, a story which is backed up by several witnesses of her own. When the Lieutenant goes to her apartment to further question her, he finds identical twins, Ruth and Terry (both played by de Havilland). They freely admit that one of them was at Central Park and one of them was with the murdered man, but they won’t say which is which, making it impossible for him to serve an arrest warrant or even one for obstructing justice.
The Lieutenant enlists the help of a psychiatrist (Lew Ayres), who has his office in the same medical building and is interested in one of the girls (he is not sure which). He also just happens to be a published expert on twins. The doctor begins interviewing the girls and giving them the Rorschach inkblot test in the hopes of finding a clue to the case. The girls (who conveniently wear necklaces with huge letters spelling out “Terry” and “Ruth” throughout most of the film) both fall for the doctor, and when he shows interest in one but not the other, this drives a wedge between them. It becomes clear that men have come between them before. Soon the doctor is able to report to the Lieutenant that one of the sisters is definitely “insane—very clever, very intelligent, but insane.”
Given the title of the film and the plot, this could have been a great film noir. Olivia de Havilland’s performance is good, and gets better as one of the girls allows her neuroses to come to the surface, while the other coolly pulls tricks on her to further antagonize her. The trick photography is pretty effective, and in one mind-boggling shot, de Havilland sits on the edge of a bed tucking herself in. I have always liked Thomas Mitchell, who is best known as Uncle Billy in It’s a Wonderful Life, but his hearty, comic screen persona is out of place here. The music by Dimitri Tiomkin also seems to undermine the suspense more than add to it. Nevertheless, there are a few good scenes and a nicely shot climax, which is then followed by a sickly sweet coda.