Henry Moon is captured for a capital offense by a posse when his horse quits while trying to escape to Mexico. He finds that there is a post-Civil War law in the small town that any single or widowed woman can save him from the gallows by marrying him.

Real estate developer Jake Berman hires private investigator and war veteran Jake Gittes for some run-of-the-mill matrimonial work. After Berman shoots his wife's lover, who happens to be his business partner, Gittes is drawn into a web of conspiracy and deceit involving the oil reserves beneath Los Angeles. While investigating, Gittes hears a voice from his past that causes him to revisit a traumatic case in Chinatown.