Warning: Contains spoilers
Private eye Jake Gittes (Jack Nicholson), a successful man with a nasty reputation specializing in marital cases, is hired by Mrs. Mulwray (Diane Ladd) to investigate the alleged infidelities of her husband Hollis Mulwray (Darrell Zwerling), chief engineer of the city's water supply. Jake and his two associates follow Mulwray as he spends long hours investigating reservoirs, walking dry river beds, and staring at the ocean. The city is in the midst of a drought and he has, as Jake puts it, "water on the brain". But he's also got a mistress, who Jake discovers and photographs, only to find that the photos have instantly found their way to the newspaper and that the real Evelyn Mulwray (Faye Dunaway) is suing him. Just as quickly, Hollis is dead, and Jake finds himself in the middle of something much more complicated than photographing an affair.
But in the convoluted reality that is Chinatown, how certain can Jake be that he's actually witnessed an affair? Viewed through a zoom lens and taken at face value as validation of the job he was hired to do, it certainly looks like evidence of an affair, and that's what Jake assumes. The work is easier that way. When Evelyn asks Jake what he used to do in his previous life as a cop in Chinatown, he answers, "as little as possible," and that philosophy is one he seems to have adapted to his current line of work. The problem is that this approach leads to Jake drawing concrete conclusions — often incorrectly — at multiple points in the investigation. In a lot of ways it's a scattershot approach — he's sometimes right, sometimes wrong — and with a little more due diligence he could have the thing wrapped up quickly, but then it wouldn't be much of a film, would it?
Despite the Occam's razor methodology of finding the simplest explanation, Jake manages to get needlessly drawn into a complicated web. He puts his nose where it doesn't belong (and has the bandage to prove it). He gets involved personally with the case. He fails to take his own advice to "let sleeping dogs lie." He tells his one operative of the need for a certain amount of finesse, but fails to use any himself. This does not necessarily make Jake a bad private eye, just a headstrong one with some contrarian tendencies, almost a bull in the china shop. Still, his is a results-oriented profession and Jake manages by sheer will to get results, proving that there is a method to his madness or perhaps that he's got more finesse than we realize. He certainly isn’t the first private eye in the world to solve the case despite his methods.
Few actors could pull off a role this complex as well as Nicholson, who as the protagonist serves as the film’s ballast. Initially he appears to be playing a standard film noir private eye, but as the film progresses, he begins adding layers. He laughs a raucous laugh at a racist joke, nearly comes to blows with a bank manager, and gets into a couple of fights, which is pretty much what we expect from the character. But, he also shows tenderness and humanity where needed. He harbors no ill will toward the people who seem to be making his job more difficult, telling Russ Yelburton (John Hillerman) that he’s more than willing to pass the whole thing off on a couple of big shots.
One of the delights of Chinatown is that in this web of mystery and intrigue, the audience is never given any more information than Jake has at that particular moment, nor are we given any hint as to how reliable such information is. We know only that he has it and where he got it. Since the entire film is done from a first-person perspective, we're given no indication of the various machinations going on behind Jake's back. In essence, we are put in the position of one of his operatives, trying desperately to piece the whole thing together. Eventually we do, largely without chunks of exposition explaining the complicated proceedings and at the end of the film not only does the entire thing hold water, but it makes sense. This is no small feat for a film noir done without voiceover.
Naturally much of the credit goes to Robert Towne’s Academy Award winning script, but likely this would not have been possible without the uncredited contributions of Roman Polanski and Jack Nicholson. Nicholson wrote sections of his character’s dialogue and Polanski, faced with an original draft of over 300 pages, worked closely with Towne to trim it down to something a bit more manageable. One of the changes was to eliminate the voiceover narration, a staple of the genre, thus allowing things to flow more smoothly. The result is a wonderfully complex script where virtually every scene serves to advance either the plot or the characters, and sometimes both. Take, for example, the opening scene in which Curly (Burt Young) has just learned of his wife’s infidelities. We start by seeing the photographs — undeniable proof in this instance — and then Curly’s pained reaction. This is nothing new to Jake, who calmly offers him a drink and later assures the poor fisherman that he can pay when he’s able. We learn a lot about who Jake is, what he does for a living, and that he’s a nice enough person not to take a poor man’s last dime. The whole thing seems to be a standard enough opening to a film noir, especially when it moves seamlessly into the main investigation. But part of Towne’s genius is how he relates the scene to what happens later in the film, how Curly plays a more important role than we would have expected, how Jake’s casual comment of “What can I tell you, kid? You're right. When you're right, you're right, and you're right” is more vital to his character than we would have expected. Whereas a lot of writers would have used the scene as a simple introduction or a clumsy means of foreshadowing, Towne ties it to the story effortlessly and deftly, and it’s all the more effective because we don’t expect such a scene to have any real importance.
The title doubles as both a part of Los Angeles and a metaphorical state of mind where it can be difficult to understand what’s truly happening, where outward appearances are rarely accurate and a barrier exists between reality and the truth. It has been described as feeling like you’re always on the wrong foot, that things are constantly slightly off-kilter. It’s a place where perception is not always reality, where to get too involved can be dangerous, where it’s probably best to let sleeping dogs lie. One of Roman Polanski’s master strokes was to change Towne’s upbeat ending to reflect a fatalistic worldview. (This was Polanski’s first American film after the murder of his girlfriend, Sharon Tate, in the Manson family incident.) At the end of the day, after all his investigation, what has Jake really gained? He has the truth, sure, but he also has a scar on his nose, his car is damaged, people have died, and none of those big shots got what was coming to them. The unveiling of truth has probably done more harm than good, but that’s how things work sometimes in Chinatown.
 While this sounds like a terrible method of police work, it is actually recommended to officers in Chinatown, due to the fact that the various dialects make it dangerous to investigate every little thing that people do or say. Therefore, the approach is a more laissez-faire one than normal.  Per Wikipedia: it is translated from Latin as "entities should not be multiplied beyond necessity."  Hillerman is best known for playing Jonathan Higgins in the seminal television series Magnum, P.I. (1980-88), so he knows a little bit about dealing with a private eye.  The script won the Oscar for Best Original Screenplay, the film’s only win against 11 nominations. But, when you consider that it was up against The Godfather Part II, Lenny, and Murder on the Orient Express, thait makes a lot more sense. The other 10 nominations were: Best Actress in a Leading Role (Faya Dunaway), Best Art Direction, Best Cinematography (John A. Alonzo), Best Costume Design, Best Director (Roman Polanski), Best Editing (Sam O’Steen), Best Original Score (Jerry Goldsmith), Best Sound, Best Picture, and Best Actor (Jack Nicholson). Shockingly enough, in a showdown between Nicholson, Al Pacino, Dustin Hoffman, and Albert Finney, the Oscar went to Art Carney for Harry and Tonto. Go figure.
Starring: Jack Nicholson, Faye Dunaway, John Hillerman, and John Huston
Written by: Robert Towne
Directed by: Roman Polanski
R, 131 min, 1974, USA