Alden Pyle is a CIA agent working to install General as the new leader of Vietnam in order to stamp out the steadiy growth of rampant comunism in those parts He wins over Thomas Fowler's mistress, Phuong, after Fowler's wife in London denies his request for a divorce. Pyle inadvertedly is responsible for allowing the bombing in the square, he had intended/expected for the detonations to occur at stradegic millitary sites. Hinh, Fowler's coworker and a communist sympahiser, asks Fowler to set up Pyle for assassination since accident or not he is too blame for all the deaths. Fowler jealous that Pyle is stealing away Phuong, betraying his trust and for being a part of this carnage agrees, however he gets cold feet and tries to warn Pyle but fails as Alden is intercepted by Hinh's comrades and dragged off into an alleyway he flees but is confronted Hinh concealed behind an alleway corner who plunges a blade into his chest. The police suspect Fowler, but do not press him as Tom goes to identify his friend and does show he is genuinely ashamed in his part of his pal's demise. Phuong returns to Fowler and they remain in Vietnam through the 1960's.
SPOILED IT FOR YA!