Scientist David Bowman has retired to a tropical island, his only friend a native boy he has adopted as his own. A conscientious objector, he has no desire to choose sides in the war that has erupted in the Pacific. His pacifism makes him an easy victim for Matsuru, a Japanese secret agent who seizes his home. Matsuru uses the scientist's experimental equipment to destroy American ships while David stands by helplessly. But when the saboteur kills his adopted son, he will have to stand and fight.
Prisoner of Japan features a story from the illustrious Edgar G. Ulmer, who began his career assisting F.W. Murnau on the classic Sunrise: A Song of Two Humans (1927). On his own, he directed the Bela Lugosi thriller The Black Cat (1934). By the 1940s, Ulmer had ended up at the Poverty Row studio PRC, for whom he wrote Prisoner of Japan. He also provided uncredited second-unit work, stepping in for director Arthur Ripley (Voice in the Wind, The Chase) in the later stages of production. Two years later, Ulmer would make his best-known film, the stylish Detour (1945). Leading man Alan Baxter had studied drama with legendary director Elia Kazan. After making his debut opposite Sylvia Sidney in Mary Burns, Fugitive (1935), he scored an impressive supporting role in Alfred Hitchcock's Saboteur (1942). Perhaps spurred on by Prisoner of Japan's message, he signed up for the Army Air Force shortly after the film's release. Caucasian actor Ernest Dorian plays Matsuru, in a practice typical of wartime era films that featured Japanese villains. Under his original name Ernst Deutsch, Dorian had been one of the creators of The Golem (1920). He later had a memorable part in Carol Reed's The Third Man (1949).