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A man (Davos Hanich) is a prisoner in the aftermath of World War III in post-apocalyptic Paris, where survivors live underground in the Palais de Chaillot galleries. Scientists research time travel, hoping to send test subjects to different time periods “to call past and future to the rescue of the present”. They have difficulty finding subjects who can mentally withstand the shock of time travel. The scientists eventually settle upon the prisoner; his key to the past is a vague but obsessive memory from his pre-war childhood of a woman (Hélène Châtelain) he had seen on the observation platform (“the jetty“) at Orly Airport shortly before witnessing a startling incident there. He did not understand exactly what happened, but knew he had seen a man die.
After several attempts, he reaches the pre-war period. He meets the woman from his memory, and they develop a romantic relationship. After his successful passages to the past, the experimenters attempt to send him into the far future. In a brief meeting with the technologically advanced people of the future, he is given a power unit sufficient to regenerate his own destroyed society.
Upon his return, with his mission accomplished, he discerns that he is to be executed by his jailers. He is contacted by the people of the future, who offer to help him escape to their time permanently; but he asks instead to be returned to the pre-war time of his childhood, hoping to find the woman again. He is returned to the past, placed on the jetty at the airport, and it occurs to him that the child version of himself is probably also there at the same time. He is more concerned with locating the woman, and quickly spots her. However, as he rushes to her, he notices an agent of his jailers who has followed him and realizes the agent is about to kill him. In his final moments, he comes to understand that the incident he witnessed as a child, which has haunted him ever since, was his own death.