Jim Hetherton (Franchot Tone), the scion of an aristocratic rural English family, was traumatized from boyhood by a shooting accident and reaches adulthood as a sincere and dedicated pacifist -- like many of his generation in England. He makes his way through life as a schoolteacher with a promising future, and even ponders the possibility of marriage with Dora Bruckmann (Veronica Lake), the governess of his young nephew. But then the Second World War breaks out, which creates a crisis for Jim and his family and household. He decides that he can't a won't fight if it means killing another human being, and is accepted as a conscientious objector by the authorities. But in doing so, he is forced to give up his teaching position and take a job in farming, to contribute to the economic good at home. He soon finds himself being shunned by much of the village for his beliefs, and discovers that even amid a manpower shortage, securing a job to fulfill his service requirement is no easy matter. Meanwhile, his brother (John Sutton) is called up by the RAF, and his father (Henry Stephenson) joins the home guard. And Dora seems headed to an internment camp, until Jim marries her. But what neither he nor anyone else suspects is that Dora is actually an agent planted by the Germans, part of a team of fifth columnists working to undermine the British war effort. And her main concern is finding the location of a secret British airfield in the vicinity of the Hetherton estate. She manages to manipulate Jim by preying on his beliefs, and maneuvers him into potentially betraying his country.