Fear No More (1961) on Netflix

Plot summary

Sharon Carlin, a personal secretary, is on a train from Los Angeles to San Francisco, carrying an envelope to deliver for her employer. In her compartment a man threatens her with a gun, and a woman there appears to be dead. The man knocks Sharon unconscious. She wakes to a plainclothes policeman accusing her of murdering the woman. When they leave the train, Sharon dodges the detective and runs into the street. A car swerves to avoid her and a boy inside is slightly hurt. The driver, Paul Colbert, is the boy's father.