Alden Pyle, an undercover U.S. agent, is found murdered in French Saigon. In the early 1950’s, the French still controlled Vietnam as a colony, but they were beginning to lose control of the country to the communist revolutionaries. Pyle had come to investigate conditions and had befriended an English newspaper correspondent, Thomas Fowler. Vigot, the French police chief, orders Fowler and his former mistress, Phuong, to his office for questioning. Fowler is under suspicion because he is one of the last people to have seen Pyle alive, and Pyle had taken Phuong from Fowler.

Vigot interrogates Fowler, who proclaims not only his innocence but also his ignorance of what happened to Pyle. Phuong, who does not understand English, says nothing. After the interrogation, Fowler tells her that Pyle had been murdered. Her reaction is surprisingly mild, and she reveals almost nothing about her feelings. Fowler then goes over the sequence of events that led to Pyle’s murder and Vigot’s summons to police headquarters.

As the story goes, Pyle befriends Fowler during his first days in Saigon. Fowler is a reluctant companion. He dislikes Americans, especially ones like Pyle who seem on a mission to save the world. Pyle never admits to Fowler that he is a CIA agent—indeed no reference is made to the U.S. Central Intelligence Agency in the novel, except for Fowler’s suggestion that Pyle might work for the U.S. Office of Strategic Services (OSS). Established in World War II, the OSS was the precursor of the postwar CIA.

To Fowler, Pyle is an innocent who reads books on Vietnam but does not understand the reality of people’s lives. Fowler believes that the Vietnamese should be left alone. He does not believe that their lives could be improved by Westerners. He considers himself a reporter without political commitments or opinions. He is an older man (not saying how much older) who disdains Pyle’s idealism. Pyle wants to save Vietnam from communism. Fowler finds this attitude ridiculous and dangerous because it means Pyle would involve himself with the local Vietnamese anticommunist military, who seem to Fowler no more than gangsters. If the French were to lose Vietnam, it could not be saved by Americans looking for a “third force” (some group other than the communists or the French).

The third force is a theory Pyle had adopted from a book on Vietnam by York Harding. To Fowler, both Harding and Pyle ignored reality to pursue theory. Pyle even condones the terrorist acts of General Thé, an anticommunist thug. General Thé blew up a café, maiming men, women, and children. To Pyle, this atrocity was a mistake. He plans to straighten it out with the general. To Fowler, the atrocity proves that Pyle is doing great harm in spite of his good intentions.

On the personal level, Pyle takes Fowler’s mistress away from him because Pyle believes that Phuong has to be saved. Pyle earnestly wants to know if Fowler loves Phuong and means to marry her. When Fowler admits he is using Phuong for his selfish pleasure, Pyle offers her marriage and a home in the United States, which she accepts.

In spite of their political and personal conflicts, Fowler finds it hard to reject Pyle. On a mission to observe the war in action, Fowler is injured and Pyle risks his own life to save him. Fowler knows that Pyle means well, and Pyle complicates Fowler’s feelings about him by constantly saying he knows that Fowler is not nearly as cynical and selfish as he says.

Pyle’s dangerous innocence and idealism so outrage Fowler that he decides he...