Mr. Brown loves to play poker, but he usually loses. After another losing night of cards, he promises his wife that he'll never play again, but then one of his friends helps him pretend that he is just going to club meetings on Wednesday nights. When Mrs. Brown figures out what he has been up to, she and her cousin come up with a plan that they hope will cure Mr. Brown of his poker playing once and for all.

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.