In 1940s Los Angeles private detective Jake Gittes (Jack Nicholson) is hired to follow Hollis Mulwray (Darrell Zwerling) by a woman who claims to be his wife Evelyn (Diane Ladd). He photographs Mulwray kissing a young blonde (Belinda Palmer) and the press gets wind of it. Because Mulwray is the city’s chief water engineer this creates a scandal that opens the door to clues about even worse goings on. These include the dumping of fresh water into the ocean at night although a severe drought is raging and the building of an expensive new dam. When Mulwray is discovered dead by drowning the real Mrs. Mulwray (Faye Dunaway) hires Gittes to find out what happened. The fake Mrs. Mulwray is actually a woman named Ida Sessions who points Gittes towards the name of another man linked to Mulwray. This is Noah Cross (John Huston) who is Mulwray’s former partner and Evelyn Mulwray’s father. Cross also hires Gittes ostensibly to find the blonde girl. As Gittes delves deeper into the two cases he uncovers a crooked plot to make money by manipulating the water supply and some very nasty family secrets.