California cowpuncher Jim Kern and his pal enlist in the war against Germany and, shortly thereafter, meet Frank Akuri, who has pledged to colonize the United States for his homeland, Japan. While Jim and other white males are fighting in France, Akuri forces Jim's sweetheart Mary to sell her ranch, as she is not able to run it because the only men left, the Japanese, have pledged not to work for the whites. With the ranch, Akuri begins his colony. Mary counters by organizing her society women friends to appeal to Congress against the "yellow menace." When it seems that his plans will be thwarted, Akuri issues orders for the death of Mary and her friends, but Jim and his pal return and rescue them. Akuri then kidnaps Mary and takes her to his apartment, but with the help of Akuri's wronged Japanese lover, Jim learns her whereabouts. He organizes a posse of American Legion locals and rescues Mary just as Akuri is about to murder her. Akuri's group is routed out.