I can’t think of a purer cinematic interpretation of the modern private eye story: the detective starts with an apparently simple case that leads him to discover a much greater conspiracy or crime, which can only be untangled or resolved by getting to the heart of the original mystery.
Polanski tells the story in a slow and measured fashion. There is no rushing around from action scene to cliffhanger to fight sequence, as would be required in a Hollywood detective film today. J.J. Gittes (Jack Nicholson) doesn’t have to be a buffed-up hero; he just has to stand up for his principles, and try to uncover the truth. His moral code binds him to the plight of Evelyn Mulwray (Faye Dunaway), and compels him to take his investigation all the way to its inevitable conclusion, no matter how much it may cost him. A beautiful film, and a deserved classic.