Michael Bachlin, an apolitical doctor with the United Nation's World Health Organization, is in Shanghai investigating a missing shipment of medical supplies and finds he must travel to Peking on the express train. Among the other passengers on board are a priest, Father Joseph Murray, who has been in China for many years, and Kwon, a mysterious businessman. Just before the train leaves, Kwon’s son, Ti Shen, attempts to join him, but his mother, Li Eiu, has Ti Shen taken into custody by Nationalist agents, then boards the train herself. Once the train leaves Shanghai, Michael encounters former lover Danielle Grenier, a nightclub singer he knew five years earlier in Paris, but who he now believes betrayed him. Kwon has seen Danielle perform and invites her and Michael to join him in the dining car. When Father Murray sits down at the same table as Wong, a reporter and ardent Communist, Wong accuses the priest of being an enemy of the people and joins Michael and the others. Wong then becomes involved in a political argument with Michael, and after Wong leaves the table, Murray joins them and talks about his great affection for Peking. Later, after Danielle tells Michael that she married after they broke up, but lost her husband a year earlier, they discover Kwon beating his wife, who is sharing Danielle’s compartment. The next day, while the train stops to pick up some soldiers, Kwon passes a message to a vendor, who takes it to be telegraphed. Michael, meanwhile, has a change of heart about Danielle and asks to resume their romance, but she declines, citing her involvement with many men. When Li Eiu is discovered with a knife wound, Kwon claims that she attempted suicide, but Michael thinks otherwise and says that she will recover. The train then is forced to halt by a blocked line, and is ambushed and attacked. The soldiers on board surrender, but are shot. After Michael, Danielle, Murphy and Wong are removed from the train, Wong states that the ambushers must be counter-revolutionary forces. The group is loaded onto a truck and taken to a nearby base camp at a farm house, where they discover that the man in charge of the operation is none other than Kwon. Kwon admits he has deviated from the Communist line and regards himself as an independent entrepreneur dealing in the black market, including much-needed medical supplies. Kwon reveals that he knows Michael is going to Peking to treat an ailing general in the Nationalist underground and says he is going to contact the underground in Peking and offer to release the train and its passengers in exchange for the release of his son. Danielle confesses to Michael that she has been working as a spy and that her late husband was a Communist. In a radio communication with the Nationalists, Michael is forced to read Kwon’s instructions for the release of his son. Ti Shen is to be flown in to the base-camp, but if the plane is followed, all the hostages will die. After Wong accuses Kwon of treachery, Wong is tortured and his hands are burned with a poker. Later, after Ti Shen’s plane arrives, the pilot radios Peking that he will leave at dawn with Michael, at which time Kwon is to release the train. However, Kwon shoots and kills the pilot. Michael treats Wong’s wounds, and the reporter begins to realize that Michael’s work is truly humanitarian and not political. Ti Shen is dismayed by his father’s actions, and Michael tells him that his mother’s suicide attempt was actually an attempted murder and that she has been trying to save him from his father’s influence. Meanwhile, Kwon has been lusting after Danielle and suddenly tells Michael that he can leave on the train with Murray. After Danielle tells Michael that she will be staying with Kwon as he has money and he does not, Michael walks away from her in disgust. Kwon orders Danielle to collect her luggage from the train, and later, Li Eiu, clutching her wound, makes her way from the train to the camp and confronts Kwon, accusing him of turning their son against her. She stabs Kwon twice, killing him, then collapses. Ti Shen discovers his parents and summons Michael. With her dying breath, Li Eiu begs Ti Shen to renounce the shameful life he has led and help Michael to escape. Using Kwon’s gun, Michael takes Ti Shen hostage and they drive back to the train. There, Michael tries to find Danielle, but she has already returned to the farmhouse. Michael then ties up Ti Shen, leaves him in Murray’s custody, returns to the base, shoots two guards and orders Danielle into his vehicle. As the train pulls out, Wong and two soldiers pursue it in a jeep, firing on it. Wong throws a hand grenade, which injures Murray, but Michael returns fire with a machine gun, killing all three. More soldiers pursue them as Michael examines Murray. After telling Michael how to recover the medicine shipment that his father had stolen, Ti Shen picks up the machine gun, fires on the soldiers and is killed while successfully fending them off. Murray tells Michael that Danielle had agreed to stay with Kwon in order to save Michael’s life, and she and Michael reunite. Michael then assures the priest that he will recover to see Peking again.