Measure for Measure (1979)

When the Duke of Vienna takes a mysterious leave of absence and leaves the strict Angelo in charge, things couldn't be worse for Claudio, who is sentenced to death for premarital sex. His sister, Isabella (a nun-in-training), however, is a very persuasive pleader. She goes to Angelo, but instead of freeing her brother, she gets an offer from Angelo to save Claudio's life if Isabella sleeps with him.