The brother of Jeanne Masson, a young nightclub singer, has been murdered by Brasier, a criminal who pretends to be a respectable man. Jeanne has resolved to avenge her brother but she just cannot take action herself. The way she finds is to ask police detective Pierre Leblanc to help her do it. Pierre gives his agreement and starts following the trail. He soon finds out that Brasier belongs to a gang whose boss, Cortedani, has ordered the murder.