Eerie music plays as the opening credits roll, before modulating into melancholy jazz.
Startlingly, the scene switches to a guy in a private eye's office, flipping through pictures of a woman having sex with another man outdoors.
As the guy throws down the pictures in disgust and anger, and starts weeping, we realize that these were pictures of his wife with her lover.
The private eye tells him to control himself, and then pours a drink for him.
The private eye sees him out, and he is identified by the name Jake Gittes.
Jake goes back into his office to see his next client, Mrs. Mulwray—a somewhat older woman who says her husband is seeing another woman. Jake unrealistically feigns surprise.
Mrs. Mulwray says she has an intuitive sense that her husband is cheating on her, but Jake tells her that if she loves him—and she says she does—she should just go home.
But Mrs. Mulwray's determined to know what's going on. She reveals that her husband, Hollis Mulwray, is chief engineer for the Department of Water and Power.
The scene shifts to city hall, where a speaker's discussing how L.A. badly needs water (since it's essentially a desert community). His call for a new deal to bring water to the city is met with cheers.
Another speaker takes the stage and explains that doing more engineering work would cause flooding and a busted damn. This is Hollis Mulwray.
The crowd in the courthouse boos him, and a farmer lets his sheep into the hall, yelling at Mulwray and accusing him of conspiring to starve their livestock and crops, keeping the water in the hands of a powerful few.