No Man of Her Own (1950), directed by William Leisen, starring Barbara Stanwyck, is a rare instance of a movie that is as good as the book its based on.
I enjoyed the book, I Married a Dead Man by Cornell Woolrich. The opening chapters set up a tall tale: a pregnant woman meets another pregnant woman on a train; the train crashes and one of them dies; the one who lives is mistaken for the one who died.
The rest of the book plays out this premise. The survivor reluctantly accepts the new identity thrust upon her because her own prospects as an unmarried mother are grim, whereas the other woman was a newlywed mother on her way to meet her husband's wealthy family.
Once past this unlikely premise, the suspense mounts steadily as the mother lives a lie for the sake of providing a better life for her child. It's a classic noir dilemma: doing a bad thing for a good reason.
The film makes the premise easier to believe thanks to Leisen's efficient visual style. The director's craft is evident throughout the rest of the film as well. He frequently lets Stanwyck's face tell the story in long close-ups.
If you go looking for this film, don't confuse it with another film of the same title made in 1932, starring Clark Gable and Carole Lombard. Also, don't be mislead by the film's credits, which say it is based on the book by William Irish. Woolrich originally published I Married a Dead Man under a pseudonym.