Fred C. Dobbs and Bob Curtin, both down on their luck in Tampico, Mexico in 1925, meet up with a grizzled prospector named Howard and decide to join with him in search of gold in the wilds of central Mexico. Through enormous difficulties, they eventually succeed in finding gold, but bandits, the elements, and most especially greed threaten to turn their success into disaster.

In 1938, Walter Neff, an experienced salesman of the Pacific All Risk Insurance Co., meets the seductive wife of one of his clients, Phyllis Dietrichson, and they have an affair. Phyllis proposes to kill her husband to receive the proceeds of an accident insurance policy and Walter devises a scheme to receive twice the amount based on a double indemnity clause. When Mr. Dietrichson is found dead on a train-track, the police accept the determination of accidental death. However, the insurance analyst and Walter's best friend Barton Keyes does not buy the story and suspects that Phyllis has murdered her husband with the help of another man.