Doctor Michael Bachlin (Joseph Cotten), is in Shanghai investigating a missing shipment of medical supplies for the United Nation's World Health Organization. He must travel to Peking on the express train with other passengers, Father Joseph Murray (Edmund Gwenn), and Kwon (Marvin Miller), a mysterious businessman. Just before the train leaves, Kwon's son, Ti Shen (Robert W. Lee), attempts to board, but his mother, Li Eiu (Soo Yong), has him arrested by Nationalist agents, before boarding the train herself.