Set in 1938 Los Angeles, smooth-talking insurance salesman Walter Neff crosses paths with Phyllis Dietrichson, a seductive housewife whose wealthy husband, Barton, has an auto-club policy up for renewal. Phyllis immediately sets her sights on Walter, manipulating him into a lethal scheme to murder her husband and collect on a lucrative
accidental death benefit that includes a double indemnity clause, which pays out double for freak accidents.Though initially hesitant, Walter is blinded by lust and seduced by Phyllis, soon devising a foolproof plan. He intends to murder Barton and make it appear as though he fell from a moving train. To pull this off, Walter impersonates Barton to board the train, while an accomplice actually kills the older man. However, the plot immediately encounters complications. Barton wears a heavy plaster cast on a broken leg, making his supposed journey awkward, and a suspicious neighbor catches a glimpse of the impostor.Arthur Jackson, the company’s dogged claims investigator and Walter’s close friend, smells a rat from the beginning. Convinced the death is neither accidental nor suicide, Jackson refuses to pay out the claim, focusing intently on the suspicious circumstances surrounding the policy change and the elusive blonde widow. As
the investigation tightens, the passionate facade between Walter and Phyllis rapidly fractures. Walter discovers that Phyllis has a history of violence and manipulated him merely as a disposable pawn, while Phyllis realizes Jackson is closing in. Paranoia takes root, turning their romance into a deadly game of mutual distrust.Desperate to escape the closing net, Walter plots to eliminate Phyllis before she turns on him entirely. He arranges a late-night rendezvous at her home. Phyllis shoots Walter during the confrontation, but her lingering affection—or perhaps cowardice—prevents her from delivering a fatal second shot. Walter manages to wrest the gun away and shoots her dead, realizing too late that they were both doomed from the moment they met. Mortally wounded, Walter crawls back to his office to dictate a full confession into a dictaphone for Jackson to find. He collapses on the floor just as Jackson arrives, ensuring that their meticulously planned crime ultimately crumbles under the weight of greed, betrayal, and relentless justice.