In many ways, this film reminds me of the Maxim Gorky play "The Lower Depths" combined with the weepy films about motherhood and sacrifice Hollywood was so fond of making in the 1920s and 30s--such as "Madam X" and "So Big". None of this is meant as criticism--just an attempt to categorize this Mexican film.
The story begins in a cantina in the seedy part of town. Before Violeta (Ninón Sevilla) goes on to sing for the crowd, she goes about this nightclub trying to get the other working girls there to help contribute. It seems that one of their own is about to give birth and her good for nothing pimp boyfriend wants nothing to do with the baby. After doing the right thing and helping the young mother, Violeta's efforts are rewarded by the mother tossing the baby in the garbage! Violeta, despite her circumstances, is a good sort and rescues the boy. She could take it to the orphanage, but that's much of a life for the kid, so she spends the next several years sacrificing for the boy she takes for her own. The rest of the story is often violent, sad and extremely, extremely sentimental.
The film is interesting because on one hand it's very old fashioned and a bit schmaltzy. But on the other, it's brutal in its realism and often pulls no punches. The overall effect is a film you can't help but admire and it's a wonderful portrait of someone who manages to both prostitute herself to stay alive yet somehow maintain her humanity. Well worth seeing.