Following a rail disaster, a prostitute takes in an orphan but will have to fight to obtain the right to adopt her.

In the 1950s, young prostitute Mara travels by train with a foreign couple and their little girl, but a terrible collision with a freight train kills the parents and Mara takes the child with her. She would like to adopt her, but her social condition prevents her. She places the girl in an orphanage run by nuns and decides to leave her current life, even if it means earning less money and working in exhausting conditions. She also gets rid of Carlo, a kind of small-scale pimp. Mara has a hard time finding a decent job because the morality police keep following her. She appeals to the police commissioner who helped her place the girl in boarding school, and he finds her a factory job. But Mara's past emerges in the person of her first love, Giulio, who is convinced that the child Mara has is his daughter.