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' wife. Mr. Mulwray spends most of his time investigating dry river beds. 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 in a kiss, which becomes a scandal in the press.