JJ 'Jake' Gittes is a private detective who seems to specialize in matrimonial cases. He is hired by Evelyn Mulwray when she suspects her husband Hollis, builder of the city's water supply system, of having an affair. Gittes does what he does best and photographs him with a young girl but in the ensuing scandal, it seems he was hired by an impersonator and not the real Mrs. Mulwray. When Mr. Mulwray is found dead, Jake is plunged into a complex web of deceit involving murder, incest, and municipal corruption all related to the city's water supply.