Sister Marie-Thérèse tries to save the prostitutes doomed to a sad fate. Two of them, Marcelle and Maria, are in love with two honest men, a painter and his best friend. But the girls pretend that they work by night in a post office .An old hooker is killed by a pimp and Marcelle is a suspect .The painter could provide her with an alibi, but she does not want him to testify in her favor, as he would know who she really is.