Cardinal Richelieu and his power-hungry entourage seek to take control of seventeenth-century France, but need to destroy Father Grandier - the priest who runs the fortified town that prevents them from exerting total control. So they seek to destroy him by setting him up as a warlock in control of a devil-possessed nunnery, the mother superior of which is sexually obsessed by him. A mad witch-hunter is brought in to gather evidence against the priest, ready for the big trial.

This film was banned from Italy and its stars Vanessa Redgrave and Oliver Reed were threatened with three years' jail time if they set foot in that country. Reed described this as his best performance ever.

Jeanne:
Satan is ever ready to seduce us with sensual delights.

Continuity: Judith Pariss character is referred to as Sister Agnes in the film but listed as Sister Judith in the credits.