In Los Angeles in 1948, Julius "Jake" Berman hires private investigator J. J. "Jake" Gittes to catch his wife, Kitty, in the act of committing adultery. During the sting, Berman kills his rival, who also happens to be his business partner in a real estate development company. Gittes, not having known this, suddenly finds himself under scrutiny for his role in the possible crime, all of which centers around a wire recording that captured the illicit love meeting, the confrontation, and the killing of Mark Bodine. It calls into question if Berman knew and killed his partner to wrest control of the partnership, making it murder, or was an act of jealousy, which may qualify as "temporary insanity" and be permitted as a defense to a charge of murder.