Tristan is a police officer in the B.A.C. of Evry-Courcouronnes. One evening on patrol like any other, he calls out to a man and discovers to his amazement that he is a carbon copy of him. Troubled, the young man then tries to hide this strange apparition from those around him. But his double follows him and seeks to interfere in his life, to the point of taking his place with disconcerting ease.