In 1941, an American aviator, 'Smilin' Jack' Martin wishes to resign as an advisor to the Nationalist Chinese Army in order to return to the United States to enlist as an aviator in America's military buildup prior to the attack on Pearl Harbor. He is delayed when the Chinese discover that the neutral Tibetan like Mandon "Province" contains a secret road from India to China crucial for the Allied war effort. Determined to obtain the secret for themselves, or equally determined to have the secret destroyed is the Japanese espionage organisation "The Black Samurai" and the German intelligence agent Fräulein von Teufel who masquerades as an American newspaper reporter.