The film is prefaced by the journalist Alistair Cooke informing us that what we are about to see is all true. It is adapted from a case study by a team of psychiatrists on a patient with multiple personality disorder. She presented to them as three different people. The film needs this documentary style gravitas otherwise it might slip disastrously into unintentional comedy.
The story is based on the experiences of Christine Costner who actually claimed she had over twenty personalities. She challenged the veracity of the film. Of course, this is just screen melodrama. The psychiatrist Doctor Luther (Lee J. Cobb) ultimately cures Eve through some extremely unconvincing but convenient Hollywood Freud. But it is fascinating and fabulously entertaining.
The film leans heavily on the performance of Joanne Woodward who deservedly won a Best Female Actor Oscar. Without her credible portrayal it would be too difficult to suspend disbelief. She plays three working class characters from the southern states. Eve White is a repressed introvert. Eve Black is an extroverted good-time girl. Jane is a kind of balancing superego. Woodward slips with fluidity between the characterisations.
Director Johnson doesn't make much of the cinemascope and it's not a visually impressive film. He was a screenwriter, and he does tell the story very well. There is some comedy when the husband explores the possibilities of being married to multiple personalities. But if the film threatens to become frivolous, there is a solemn narration to redress the balance. It does touch on the personal cost to the family of mental disability but this is chiefly an addictive, outré melodrama.