In a 1940s British prison, the public executioner, Eddie Mendover, prepares for his final job before retirement. He is surprised when the condemned man, Olaf Tyson, recognises him. Mendover confesses that his real name is Eddie Tribe, and he begins to narrate the events that have led to him conceal his true identity:

Nine months earlier. Eddie's estranged father has died, leaving him the family barge business. Eddie has had little affection for his father but decides to take responsibility for the business, recruiting old seaman and long-term friend Bill Shackle as his chief crewman. Eddie's inheritance adds another dimension to an existing double identity. Using the name Eddie Mendover, he has served as H.M. public executioner, covering this role as the owner of a modest barbershop in the East End. Only Ron, the shop assistant, knows of his job as hangman.

Eddie meets Frankie, a sometime dancer with no family and lonely to the point of depression. Seeing an opportunity for companionship, she accepts Eddie's advances and before long they are planning to marry. Eddie passes over the barbershop business to Ron without explaining his new circumstances. Surprised at the gesture, Ron talks Eddie into keeping the shop keys in case he ever needs to return.

Eddie and Frankie are happy in the first months of marriage and settle on his father's old barge. The business is booming and Eddie decides to employ a second crewman. Olaf Tyson, a young Danish drifter proves to be an able seaman and Eddie offers him work, despite Bill's reservations. Eddie has given notice to retire as hangman, but is required to stay on for six months while a replacement is found. He is obliged to keep his execution appointments, but continues to keep his identity hidden from Frankie, travelling overnight on the pretext that he is attending meetings about the barge business. Olaf is ever-present and begins to take advantage of Eddie's absences to try to seduce Frankie. She rejects him and pesters Eddie to stop going away overnight. Eddie lets Frankie know that his engagements will end soon and gives her a gun to help her feel secure.

As summer continues, Olaf continues to pursue Frankie. He discovers her passion for dancing and offers to take her to a dance hall. Frankie relents and risks an evening with Olaf when Eddie is next away. At the end of the night, she tries to send Olaf home but during a final dance he forces himself on her.

Eddie returns feeling refreshed - he has one final appointment before his retirement. In his enthusiasm, he agrees to continue Olaf's contract and signs his visa. Full of confidence, Olaf begins to taunt Frankie about the secret of their night together. Frankie pleads with Eddie to take her with him but, desperate not to reveal his secret identity, Eddie declines. He reassures her that his next engagement is his last.

On the night of the final execution, Olaf threatens Frankie into allowing him to stay over, but Eddie makes an early return home and finds the young couple together. Locking Frankie inside the barge, he fights with Olaf. A clumsy scuffle ends with Eddie being thrown overboard. With his body missing, Frankie calls for help and soon Olaf is arrested for murder. During questioning, the police pressure Frankie to admit that Olaf was her lover. In a moment alone, Frankie uses the gun Eddie gave her to shoot herself, her humiliation and loss too much to bear.

Later that evening, an unconscious Eddie awakens on the riverbank. He discovers a set of keys in his pocket and makes his way to the barbershop. Ron looks after Eddie, unaware of his misfortune. Eddie resumes his Mendover identity, following the barge murder hunt from afar. Distraught at Frankie's death, he resumes his execution responsibilities, in the hope of exacting revenge on Olaf. Only when Olaf's recognises Eddie does he admit that he is the 'murdered' Eddie Tribe, acknowledging that his vengeance would never bring Frankie back.

The following morning Ron returns to the shop to find Eddie hanging.