Spoiler warning: Plot and/or ending details follow.
Set in Saigon, Vietnam in the early 1950s during the end of the First Indochina War, it portrays two concurrent conflicts: a romantic triangle between the veteran British journalist Thomas Fowler, the young American Alden Pyle, and Fowler's Vietnamese girlfriend Phuong; and the political turmoil and growing American involvement that led to the Vietnam War. Fowler, who narrates the story, is involved in the war only as an observer; his experiences are partly based on Greene's own years in Vietnam. Pyle is more directly involved on a number of levels, and Greene draws parallels between Pyle's conduct and America's overall policies in Vietnam. The turning point of the story involves an effort by the U.S. to build up a corrupt militia leader, General Thébased on the actual Trinh Minh Theas a "Third Force" against the Viet Minh. A series of terrorist bombings in Saigon, blamed on the Communists, are used to justify Thé's takeover of the city; similar nonfictional events took place in 1952 while Greene was in Saigon. Greene believed (and it was soon confirmed) that the bombings were in fact engineered by Thé as a pretext, with the cooperation of American advisors. In the novel, Fowler's discovery of this thinly concealed plot leads him to his one political act, arranging for Pyle's death at the hands of the Communists, which resolves both the romantic triangle and Fowler's disgust with Pyle's destructive idealism. Spoilers end here.
The Quiet American (film) - The 1958 film adaptation
The Quiet American (2002 film) - The 2002 film adaptation