Although it seems that Phuong is in love with the older Fowler, she above all else desires to marry a Westerner so that she may move to their country with them. The problem is that Fowler is already married; and because his wife is a devout Catholic, he has not been able to divorce her and marry Phuong. This lead to Phuong leaving Fowler for Pyle, who she will be able to marry and then move to the U.S. with.
While all of this is going on, a "third power" (not French and not Communist) arises in Vietnam in the person of a General The. Pyle lets it be known that he supports this man and his cause since he believes that colonialism is not the answer to the problems in Vietnam, but Communism is not either. This seemingly noble idea runs into the fact that since the new general's rise to prominence, there has been an increase in atrocities (more like terror attacks) throughout the country that the West is blaming on the Communist forces. Fowler soon discovers that the "third power" The is behind these attacks, with American aide, in hopes of acquiring even more aid from the U.S.
Fowler then finds out that Pyle is not truly an aide worker, but really a CIA undercover operative sent to the country to find such a "third power" and assist in the rise of it, by means of the aforementioned terrorist attacks. Thus, Pyle had been complicit (directly or indirectly) in all of the killings of innocents that had been taking place. Once he finds this out, he agrees to assist his Vietnamese contacts assassinate Pyle.
The movie ends with Pyle getting stabbed and killed, and then Phuong returning to Fowler, who promises her that he "will never leave" Vietnam or her.
Links
- http://www.amazon.com/The-Quiet-American-Michael-Caine/dp/B00005JLXB
- https://www.corbettreport.com/?s=gladio+b - For more on the staging of terrorist attacks in foreign countries by the CIA in the furtherance of their objectives, please research "Gladio B"