The Breach (1970)

Helene Regnier's husband Charles, who is mentally ill, injures their son Michel in a rage. Charles moves back in with his wealthy and manipulative parents, who blame Helene for their son's condition and vow to win custody of Michel. While the boy is in hospital, Helene rents a room in a boarding house nearby. The Regniers hire Paul Thomas, a family acquaintance who needs money, to find dirt on Helene before the court hearing on custody. Paul moves into the boarding house and, with the help of his girlfriend Sonia, who rarely wears clothes, plots to ruin Helene's reputation and then her very life.