In 1952 Saigon, Thomas Fowler, a seasoned correspondent for The Times (London) who has been covering the French-Communist conflict in Vietnam, is summoned to Inspector Vigot’s office to identify Alden Pyle, whose body was found floating in the Saigon River. After identifying the corpse at the morgue, Fowler crosses the newly poured cement floor in the hallway of his house and tells his young Vietnamese mistress, Phuong, that Pyle has been assassinated. Fowler then recalls the first time he met Pyle, on the terrace of the Hotel Continental in Saigon, a hotel frequented by Americans: Pyle, an idealistic young American who believes that he can “make a difference” in the war-torn country, eagerly introduces himself to Fowler as a member of the medical division of an economic aid mission. Fowler, who prides himself on being a dispassionate reporter of events, is amused by the American’s certainty that he can make things better. Later at his office, Fowler’s assistant Hinh hands him a telegram from his London editor ordering his return to England. To justify staying in Vietnam, Fowler decides to write a story about Phat Diem, a village in the North under siege by Communists. That night at a social gathering attended by Joe Tunney of the American Delegation, Fowler introduces Phuong to Pyle, who is enchanted by her beauty. After Pyle is dragged to a brothel by Bill Granger, a drunken, crude American, Fowler comes to his rescue and invites Pyle to join him and Phuong for dinner at the L’Arc en Ciel dance hall. There the naïve Pyle is shocked as American men vie to buy tickets to dance with young Vietnamese women. While dancing with Phuong, Pyle says that he knows only two words of Vietnamese. Phuong’s avaricious older sister, Miss Hei, joins them at the table, and upon learning that Pyle is unmarried, suggests that he visit her and Phuong while Fowler is away. After leaving the women, Fowler tells Pyle that when he met her, Phuong, the daughter of a good family, was forced to work as a taxi dancer after her father’s death left her penniless. Upon returning home that night, Fowler tells Phuong that he has been called back to London. When she asks to go with him, he declares that he would marry her if he could, but warns that his Roman Catholic wife will never grant him a divorce. Some time later, as Fowler nears Phat Diem, he is surprised to see Pyle, who claims that he came to get a “first-hand look” at his medical team. When they find the villagers massacred and the ground littered with dead bodies, Fowler’s French escorts blame the Communists for the murders, but Fowler questions what motive the Communists would have to kill innocent villagers. That night, they take shelter in a bunker where Fowler asks Pyle his real reason for coming. Pyle replies that he has fallen in love with Phuong and wants to “protect her.” Upon awakening the next morning, Fowler finds a note from the departed Pyle, stating that he will talk to him about Phuong in Saigon. When Fowler returns to Saigon he files his story, then watches in dismay as a rally is held to honor General Thé, a Vietnamese warlord who has broken allegiance with the French and thus is being hailed as the leader of a new political party. On the outskirts of the rally, Pyle looks on approvingly. Later, Pyle comes to the house to propose to Phuong, infuriating Fowler. After Pyle leaves, Fowler writes a letter to his wife, asking for a divorce. Months later, Fowler crosses a dangerous stretch along the Cambodian border to interview Thé and is surprised to see Pyle, who explains that he has set up camp with his medical team. When Thé refuses to meet with Fowler, Pyle arranges an interview in which Muoi, a Vietnamese businessman, translates. After Fowler implies that Thé was responsible for the massacre near Phat Diem, Thé becomes enraged and storms off. Fowler then spots Joe lurking in the shadows. Pyle unexpectedly asks Fowler for a ride back to Saigon, and as night falls, their car runs out of gas, leaving them stranded. Nearby is a watchtower being guarded by Vietnamese soldiers, and Fowler and Pyle take refuge there. Later that night, they hear cars approach and a voice calls out to the soldiers to turn over the foreigners. Grabbing one of the soldier’s rifles, Pyle jumps down from the tower and urges Fowler to follow. Fowler injures his ankle in the leap and Pyle drags him to safety just as their assailants fire-bomb the tower. Because Fowler is unable to walk, Pyle leaves him to go in search of help. While he is alone, Fowler recalls the first time he saw Phuong at the L’Arc en Ciel as she was being pawed by crass Americans. His reverie of Phuong is interrupted when Pyle arrives with some French soldiers. Upon returning to Saigon, Fowler becomes alarmed by the sudden growth of Thé’s army and begins to suspect that Joe and Muoi are backing the general. Phuong welcomes Fowler home and hands him a letter from his wife in London, which he opens and hides under his pillow when Pyle arrives unexpectedly. Fowler then announces that his wife has granted him a divorce. Some time later, Pyle, Phuong and her sister come to Fowler’s office, where Phuong’s sister confronts him with the letter in which his wife has stated that she will never grant him a divorce. Affronted, they accuse Fowler of lying and leave. When they depart, Hinh informs Fowler that he and some associates have learned that Muoi has been avoiding customs on the goods he imports. When Hinh states that a new shipment has just arrived at Muoi’s warehouse, Fowler and Hinh break into the warehouse and find containers labeled “diolacton” with Joe Tunney as their designated consignee. Returning home to find that Phuong has left him for Pyle, Fowler proceeds to Pyle’s office and then his house, where he stands forlornly in the street. Later, when Fowler asks Pyle about diolacton, Pyle says that it is a plastic used in the manufacture of eyeglasses. Soon after, Fowler is seated on the terrace of the Continental Hotel when a violent explosion rocks the square, killing and maiming innocent civilians. Horrified, Fowler runs into the carnage to help the injured while Pyle coldly observes from a distance and wipes a patch of blood from his pant leg. Back at his office, Fowler is recalling the horrific experience to Hinh when he realizes that he saw Pyle speaking fluent Vietnamese. When Fowler researches diolacton and discovers that it is used in making explosives, he realizes that the Americans are supplying Thé with the materials to make bombs. Emboldened, Hinh informs Fowler that Pyle works for the CIA and asks him to set up a meeting to which the unsuspecting Pyle will come without his bodyguards. When Fowler hesitates, Hinh counsels that “one must take sides if one is to remain human.” Consequently, Fowler invites Pyle to his house, and when Pyle arrives with his dog, he fervently defends Thé as the one person who can stop Communism and then admits that the general ordered the assassination attempt on Fowler. Appalled by the American’s arrogance and certainty about what is right, Fowler decides to aid Hinh in his plot and arranges to meet Pyle at a restaurant that night. Later that evening, Fowler is seated at an outdoor restaurant as Pyle crosses a bridge with his dog and is accosted by knife-wielding assailants. As the assailants pursue Pyle into the dark alleyways, a drunken Granger plops down at Fowler’s table, saddened by his son’s recent diagnosis with polio and desperate to talk to a familiar face. Unnerved by the turn of events, Fowler excuses himself and sees Hinh ride off on his bicycle. Late that night, after Vigot has summoned Fowler to identify Pyle’s body, Vigot comes to Fowler’s house and states that he has proof that Pyle was there earlier because Pyle’s dog, whose throat was slashed, had wet cement from Fowler’s floor between his toes. After responding that “there is a war on and people are dying every day,” Fowler goes to L’Arc en Ciel and buys a ticket to dance with Phuong. Phuong is unresponsive until Fowler promises never to leave, after which she embraces him. Once at home, Fowler tells Phuong that he needs to apologize, and she replies “not to me, never to me.”