The plot is set in a French prison, where a prison guard takes voyeuristic pleasure in observing the prisoners perform masturbatory sexual acts. In two adjacent cells, there is an older Algerian-looking man and a handsome convict in his twenties. The older man is in love with the younger one, rubbing himself against the wall and sharing his cigarette smoke with his beloved through a straw.

The prison guard, apparently jealous of the prisoner's relationship, enters the older convict's cell, beats him, and makes him suck on his gun in an unmistakably sexual fashion. However, the inmate drifts off into a fantasy where he and his object of desire roam the countryside. In the final scene, it becomes clear that the guard's power is no match for the intensity of attraction between the prisoners, even though their relationship is not consummated.

Source : Wikipedia