This French prison drama focuses on a penitentiary inmate known as the Mute, who either cannot or will not speak, even though he can apparently hear well enough. When the Mute's cellmate escapes, both the Warden and the Chief Guard try to get him to tell what he knows about the disappearance -- the Guard through violence, the Warden by transferring him to a new cell with four other prisoners and cutting off TV privileges to the inmates until the Mute spills the beans. One of the Mute's new roommates is a white collar criminal who has just landed in prison and is not dealing well with the pressures of life behind bars, but his skills with computers make him a very usefully ally among the prisoners. Meanwhile, Flic, a self-important police detective, is investigating the escape of the Mute's cellmate and is not happy with the low level of cooperation among the prison's population.

En pleine nuit, deux hommes courent au-dessus des barbelés d'une prison. Serait-ce une tentative d'évasion ? En tout cas, stupéfaction de tout le personnel, du maton chef au directeur en passant par les détenus quand l'un des deux fuyards réintègre sa cellule. Tous vont tenter de résoudre cette énigme d'autant plus difficile que l'homme n'a jamais prononcé un mot depuis son incarcération. Cet évènement extraordinaire met la prison et ses occupants sens dessus dessous.