Peter Roma, who is carrying a precious amulet to San Francisco, is shot down over China by former Russian agent Igor Sargoza, who wants the amulet because it is the key to the release of five million dollars. Peter then entrusts the amulet to his sister Irene, who teaches at a Chinese mission, hoping that she will complete the journey for him. In Shanghai, at the beginning of her journey, Irene is almost kidnapped by Sargoza, but is rescued by brash young American newspaper photographer Johnny McGinty. When Irene learns that only American citizens can be evacuated from war-torn Shanghai, her friend Howard Barclay suggests that she arrange a marriage of convenience with McGinty, to which he agrees. Upon their wedding, however, Fuji Yokahama, the head of the Japanese secret service, alters a gift sent to her by a Chinese friend, a Mandarin incense burner, by filling it with dynamite. Sargoza lights the burner and is blown up. Yokahama, who thought that the amulet was in the burner, leaves, satisfied that it will not be used to claim the five million dollars to buy arms for China. After he leaves, it is revealed that Barclay, who is a Chinese agent, removed the amulet from the incense burner. Because the United States has recently banned munition shipments to warring nations, Barclay decides not to go to China, and lets Johnny and Irene, who by now want to make their marriage more than just a convenience, go on to San Francisco together.