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. The only sympathetic friend Isabella has is a priest who, in actuality, is the Duke in disguise...and he has a plan.