A couple is brutally murdered. After the tragic event, their two orphaned daughters become even closer. As young adults they both work in Paris and live in the working class neighbourhood of Ménilmontant. The younger of the two is seduced by a youth. She becomes pregnant then discovers that her lover is also having an affair with her older sister. She runs away. Desperate and penniless, she wanders through the streets with her baby. Watching the prostitutes come and go, she discovers that her sister is one of them.