Stacy Keach stars as Martin Luther, a 16th-century clergyman who breaks away from the Catholic Church and sparks the Protestant Reformation. The film follows Luther's journey from his novitiate in Erfurt to his later years, including his confrontations with Johann Tetzel and Thomas Cardinal Cajetan de Vio. Julian Glover narrates the story as a young knight, who challenges Luther for abandoning the Peasants' Revolt, while Luther defends his stance on justification by faith alone.