A Los Angeles, private investigator named Jake "J.J." Gittes (Nicholson) is hired to spy on Hollis Mulwray, the chief engineer for the city's water department. The woman hiring Gittes claims to be Evelyn Mulwray, Hollis's wife. Mr. Mulwray spends most of his time investigating dry riverbeds. Mr. Mulwray also has a heated argument with an elderly man. Gittes finally catches Mulwray during an outing with a young blonde and photographs the pair, which becomes a scandal in the press. After the story is published, Gittes learns that the woman who hired him was not the real Evelyn Mulwray