Robert Towne's screenplay. Jack Nicholson's private detective. The neo-noir against which all subsequent neo-noirs have been measured.
Los Angeles, 1937. Private detective J.J. 'Jake' Gittes is hired by a woman calling herself Mrs. Hollis Mulwray to follow her husband, the chief engineer of the Los Angeles Department of Water and Power, on suspicion of an affair. Gittes follows Mulwray, photographs him with a young woman, and the photographs appear in the Los Angeles newspapers. The next day, the real Mrs. Mulwray (Evelyn) appears in Gittes's office to inform him that he has been set up and that her husband is now dead.
Gittes is drawn into an investigation that progressively reveals: a massive water-rights conspiracy involving the city's San Fernando Valley land speculators; a personal history of incest connecting Evelyn to her own father; and a powerlessness on Gittes's part to do anything about either of these once the picture is clear. The film's closing line — 'Forget it, Jake. It's Chinatown' — has been quoted as cinema shorthand for moral helplessness ever since.
Robert Towne's Chinatown screenplay is, by general critical consensus, one of the two or three greatest screenplays in American cinema. It is the most-studied script in working screenwriter education. It is the model that the term 'neo-noir' was, in part, coined to describe. Towne won the Best Original Screenplay Oscar in 1975.
What makes the screenplay foundational is its construction of misdirection across three braided layers: the surface mystery (who killed Hollis Mulwray), the middle mystery (who is behind the Los Angeles water diversion), and the deepest mystery (who Evelyn Mulwray actually is). The audience progressively understands each layer is a layer of misdirection for the next. The screenplay's structural achievement is that the deepest layer — the incest revelation — is, on rewatching, foreshadowed across every act, but not visibly so on first viewing. The film rewards multiple watches in ways few screenplays do.
The film was produced by Robert Evans at Paramount; Polanski was the director, who had escaped the 1969 Manson murder of his wife Sharon Tate by being abroad. Towne and Polanski reportedly fought about the screenplay during production, with Polanski insisting on the bleak final-act tone and Towne preferring a less-final ending.
Polanski won. The film's closing scene — Evelyn shot dead through the eye by police, her daughter taken away by her own father (the man who raped her), Gittes standing on the Chinatown street with no recourse — is the structural conclusion Polanski insisted on. It is, in retrospect, the right call. The film's argument is that knowledge does not equate to power; Gittes has solved the mystery and is, in solving it, completely powerless. The bleaker ending lands because Polanski refused to let it lift.
Jack Nicholson's J.J. Gittes is one of the most-canonical private-detective performances ever filmed. The bandage on his nose for two-thirds of the film — applied after a thug (played by Polanski himself in cameo) slices his nostril with a switchblade — is a structural costume choice. Gittes is, in the film, both physically maimed and emotionally maimed.
Nicholson plays the character at a register that distinguishes him from the Bogart-Mitchum noir tradition he is downstream of. Gittes is openly vain, openly fallible, openly capable of misreading situations he believes he has read correctly. The performance is a model of how to play competence without arrogance.