A priest (William Holden) arrives at a mission-post in China accompanied by a young native girl who has joined him along the way. His job is to relieve the existing priest (Clifton Webb), who is now too old and weak to continue with the upkeep of the church. However, Communist soldiers arrive at the mission and seize it as a command post. Their leader rapes the native girl and impregnates her, only later to realise that Communism is no good for him. In the end, the foursome flee to the border, but are pursued by Communist forces along the way.

In 1949 Catholic priests O'Banion and Bovard are constantly harassed by the Communist People's Party at their remote mission outpost in China. Adding to Father O'Banion's troubles is the mission's cook, Siu Lan, an attractive Chinese girl who makes no secret of her love for him. Under the leadership of Colonel Ho San, the Communists wreck the mission dispensary and desecrate the chapel. Ho San straps O'Banion to a chair and rapes Siu Lan; later, when she gives birth to a son, Ho San displays paternal pride but refuses to stop persecuting the priests. Only after the villagers revolt and his superiors order the killing of all Christians, including his parents, does Ho San become convinced that Communism will never solve China's problems. He decides to smuggle Siu Lan, his son, and the two priests out of the compound, but their journey is halted within a few miles of freedom by a helicopter sent to prevent Ho San's defection. Before he can be restrained, the aged Father Bovard dons Ho San's military cap and coat and drives away in the colonel's car. He dies in a spray of bullets from the helicopter, but his sacrifice enables the others to escape. Later, at mission headquarters in Hong Kong, O'Banion marries Siu Lan and Ho San and baptizes their child.