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