American aid worker Alden Pyle arrives in Saigon in the fall of 1952, at the height of the Vietnamese fight for independence from French colonial rule. Filled with zeal for his mission to help the people of Vietnam through his economic aid program and eager to learn the lay of the land from a more experienced hand, Pyle befriends London Times correspondent Thomas Fowler. Soon however, he finds himself smitten with Fowler's young Vietnamese mistress, Phuong, who is beautiful, exotic and mysterious as the city of Saigon itself. The three become swept up in a tempetuous love triangle that leads to a series of startling revelations and finally to murder.