A Freira e a Tortura (1984)

Chief of Police Rui, a happily married man of principles, is in charge of investigating Joana, a teacher who's accused of political crimes. After some false starts, he manages to arrest her, but is startled to learn that she's also a nun. The revelation doesn't alter the natural course of events: he must torture her in order to obtain a confession, and gets increasingly attracted to her.