We begin in Vietnam in the 1950s, at the height of the tension between French colonialism and local Vietnamese Communism. Thomas Fowler, a middle-aged English reporter, lives in Saigon with his ex-lover, Phuong Hei. Fowler is waiting for Alden Pyle, the young American for whom Phuong has left Fowler. After hours of waiting, a police officer calls Fowler in to the police station, where Fowler learns that Pyle has been killed and thrown under a bridge. The police inspector, Vigot, suspiciously asks Fowler what he knows about Pyle and Pyle’s death. Although Fowler explains very little to Vigot, he privately remembers his relationship with Pyle, noting that Pyle, an agent for the American government, was responsible for at least fifty deaths in Vietnam. The novel then unfolds largely in flashbacks.
Fowler remembers meeting Pyle at a bar. Pyle is young, handsome, and quiet—altogether unlike most of the Americans Fowler knew in Vietnam. Pyle works for the Economic Aid Mission, an American institution that tries to promote economic security in Vietnam. Pyle subscribes to the ideas of the political thinker York Harding, who believed that Vietnam and other Eastern nations needed a Third Force—neither colonialism nor Communism. Fowler finds Pyle naïve, but thinks that there’s something charming and endearing about his boyishness.
Shortly thereafter, Fowler and Phuong, who are still lovers at this time, go to the Continental Hotel to drink and dance. That night, Fowler thinks about his turbulent relationship with Phuong. She is much younger than he, and her sister, Miss Hei, is irritated with him for being unable to marry Phuong—Fowler is married to a woman, Helen Fowler, in England. At the hotel, Fowler is surprised to find Pyle, whom he greets. Pyle, Fowler, and Phuong move on to the Chalet, another local establishment, where Pyle, who speaks bad French, politely asks Phuong to dance. Pyle is a poor dancer, but his gallantry makes Fowler conscious of his own age and coarseness.
A few days after Pyle meets Phuong, Fowler flies out of Saigon to Phat Diem, a town where, it’s rumored, there have been Communist attacks and bombings. In Phat Diem, Fowler stays with the Lieutenant, a well-trained military officer who shows Fowler evidence of incredible violence and destruction. Fowler is reminded that he’ll probably be forbidden to publish any information about Phat Diem, since all journalistic dispatches are rigorously censored. During his time with the Lieutenant, Fowler admits that he no longer believes in God, and in fact distrusts many aspects of his Christian faith.
While Fowler is staying in Phat Diem, Pyle visits him. Fowler learns, amazed, that Pyle has tracked Fowler down in only a few days. Pyle explains that he’s fallen in love with Phuong, and that he wants to be honest with Fowler, since they’re “best friends.” Fowler is highly irritated by Pyle’s manner—he senses that Pyle thinks he’s going to “win” Phuong in the end, because he’s younger and handsomer. Pyle leaves Fowler after less than a day. Before he returns to Saigon, Fowler tells his old friend, Pietri, that he’s planning to return to England.
Several weeks after his encounter with Pyle, Fowler meets with Pyle and Phuong to discuss their romantic conflict. Pyle asks Fowler to tell Phuong, in French, that he loves her and wants to live with her, and Fowler does so. Phuong is silent, and Pyle and Fowler argue about their affections for her. Fowler claims, falsely, that he’s staying in Vietnam, and that he’s getting a divorce from his wife. Suddenly, Phuong speaks: “No,” she says. With this, Pyle leaves, acknowledging that Phuong has chosen Fowler over him.
Weeks later, Fowler journeys outside Saigon to attend a festival sponsored by the Caodaists, a religious and political group, led by the mysterious General Thé. The Caodaists fight against both the French colonialists and the native Communists. While he’s at the festival, Fowler encounters Pyle, who’s polite and warm to Fowler. Fowler offers to give Pyle a lift back to Saigon, but during the drive, their car runs out of gas.
Fowler and Pyle walk away from their car, reasoning that they can find more gasoline in one of the nearby French outposts. Fowler leads Pyle over the walls of one such fortress, where they find two Vietnamese guards, who say and do nothing—Fowler reminds Pyle that, as “disinterested” English speakers, they can largely float through Vietnam without any trouble. Pyle succeeds in taking one of the guards’ guns, and he and Fowler spend the night talking about Phuong, their sexual inadequacies, and York Harding’s mysterious Third Force, which Pyle believes to be embodied by General Thé.
Late in the night, Fowler and Pyle hear cries and shots—the Vietminh are attacking a nearby French fortress. Suddenly, there is the sound of a megaphone outside their own fortress. Fowler guesses that the Vietminh have found his car, and are telling the two guards to send down their English-speaking guests. Pyle quickly disarms the remaining guard and hands his gun to Fowler; together, they sneak down from the fort and away from the Vietminh. During the descent, Fowler hurts his leg badly and nearly dies after the Vietminh fire a bazooka at the fort. Pyle bravely carries Fowler away from the fort, and promises him that he’s going to find help. Fowler curses Pyle and tells him to leave him for dead, but within a few hours, Pyle has found a French patrol, which takes both of them to safety.
A few days after his adventure at the fort, Fowler has been discharged from the hospital with a pronounced limp. He reunites with Phuong, who informs him that he’s received a telegram from his wife. In the telegram, Helen tells Fowler that she refuses to grant him a divorce, and that she suspects he’ll get tired of Phuong soon enough. Fowler smokes opium with Phuong, and lies to her, saying that Helen has agreed to the divorce.
Fowler receives a tip from his loyal informant, Dominguez, that he should go to a warehouse owned by Mr. Chou and Mr. Heng. At the warehouse, Fowler finds plastic mouldings, which, Heng explains, Pyle has sent for processing. Fowler is unsure what Pyle is planning.
Afterwards, Fowler meets Pyle, and Pyle has discovered that Fowler was lying about his divorce. Phuong’s sister, Miss Hei, who understands English, learned that Fowler had failed to get the divorce from Helen. Fowler cheerfully acknowledges his deceptions, and reminds Pyle that lies and deception are his only weapons against a younger, handsomer man. Pyle accuses Fowler of manipulating Phuong for sex. Fowler insists that while he’s only using Phuong for her body, she’s old enough to make up her own mind what she wants.
Jumping forward to two weeks after Pyle’s death, Fowler visits Vigot. Fowler insists that he’s not engagé—in other words, he’s not politically involved with either side in Vietnam. Nevertheless, Vigot insists, Fowler has chosen sides. Privately, Fowler thinks that he’s a suffering prisoner with a life sentence.
The narrative moves back to the weeks after Pyle discovers Fowler’s deceptions. Phuong spends more and more time with Pyle, and sees Fowler only rarely. One day, Dominguez tells Fowler to look for a story at the fountain in the center of Saigon. Fowler goes there and witnesses a huge explosion. Mr. Heng, who’s also present, tells Fowler that the mouldings Fowler saw at his warehouse were used to trigger explosions across Saigon. Heng stresses that he’s only doing his job as a manufacturer, selling his services to the highest bidder.
Fowler returns to his home to discover that Phuong has moved out altogether. He runs to the American Legation, where Pyle works, to find Phuong’s sister, Miss Hei, working as a typist. She informs him that Pyle is “working from home,” and Fowler deduces that he’s at home with Phuong. Alone, Fowler weeps for the first time in years.
Fowler leaves Saigon and goes north to report on the escalating war. He witnesses French airplanes bombing innocent civilian areas, and talks with a French officer, Captain Trouin, who tells him that the French are destined to lose the war in Vietnam. Fowler tries to have sex with a prostitute, but his memories of Phuong are so strong that he finds he can’t perform in bed.
Returning to Saigon, Fowler meets with Pyle, who tells him that he and Phuong are going to be married in the United States. Fowler feels a flash of sympathy for Phuong, who’ll be out of her element in a new country. He asks Pyle to keep Phuong’s interests in mind, and adds that he must not align himself with General Thé. He also accuses Pyle of planning the bicycle bombing, an accusation that Pyle doesn’t deny.
A few weeks later, there is another bombing in a heavily colonial part of Saigon. Women and their babies are killed. Fowler, who is walking through the area when the explosion occurs, sees Pyle, and berates him for being so indifferent to human life. Pyle admits that he planned the bombing in order to eliminate some dangerous colonial officials, and didn’t count on killing others.
Once more we “flash forward” to the aftermath of Pyle’s death. Fowler meets with Vigot once again, and tells him that it was York Harding who killed Pyle, albeit from a “long range.” Vigot presses Fowler for more details of Pyle’s death, and Fowler insists that he knows nothing about it. After Vigot leaves, Fowler thinks that he did, in fact, see Pyle on the night that he died, contrary to what he’s just told Vigot.
Shortly after explosion, Fowler goes to Heng and Chou’s warehouse again, and tells them that Fowler is responsible for killing babies. Heng nods and tells Fowler that they’ll deal with Pyle soon enough. Heng tells Fowler to invite Pyle to dinner at the Vieux Moulin between 8:30 and 9:30. Before Howler leaves, Heng tells him, “One has to take sides. If one is to remain human.”
Fowler invites Pyle to his flat. There, Fowler thanks Pyle for saving his life, but reiterates that Pyle is a fool for using York Harding to enact terrorist policies. Pyle insists that the dead Vietnamese have died for a noble cause. Fowler invites Pyle to dinner, as Heng has requested, and Pyle agrees to come.
On the night that he’s supposed to meet Pyle for dinner, Fowler goes to a movie and then walks to the Vieux Moulin. There, Fowler encounters a coarse American reporter, Bill Granger, who tells Fowler that his son is sick with polio. They part, uncertainly, and Fowler wonders what has become of Pyle that night.
The final chapter takes place after Pyle’s death. Phuong has returned to Fowler, and Helen has finally granted Fowler his divorce. Even Granger’s child has recovered from his polio. Fowler realizes that his life has gotten much better since Pyle’s death. Nevertheless, he’s still suspicious that Phuong is more in love with Pyle—and America—than with him. He wishes there were someone to whom he could say, “I’m sorry.”