A religious allegory conveyed through the life and death of a donkey. Baptized "Balthazar" by three young children at the start of the film, the donkey is soon thrown into a life of successive labors and abuses at the hands of different owners.
Jacques and Marie, two children who spend summers together in a French town near Switzerland, receive a newborn donkey as a pet and name him Balthazar. A short time later Jacques' father leaves with his family for Paris, entrusting the management of his farm to Marie's father, a local schoolteacher. Some years later, Balthazar, who has been returned to his original owner, only to lead a hard life carting sand, escapes and finds his way back to the farm. Marie, now 16, adores Balthazar, and her father keeps the donkey to pull their donkey cart. Balthazar is eventually sold to the village baker. Jacques returns and, despite a lawsuit that his father has brought against Marie's father over the running of the farm, declares his love for Marie. But Marie is infatuated with Gérard, the baker's delivery boy and leader of a gang of juvenile delinquents. Gérard treats Balthazar cruelly, and he seduces Marie, whose concern for Balthazar's well-being leads her into Gérard's hands. In time Balthazar is passed on to Arnold, a drunken tramp who uses Balthazar to give rides to tourists; then to a circus, where he performs a multiplication act by stamping his feet; and eventually back to Arnold. With Arnold's death, Balthazar is sold to a corn merchant who starves and overworks him until, too sick to work, he is taken back by Marie's parents. Meanwhile, Marie has left home because of her continuing relationship with Gérard, and she offers herself to the corn merchant for a place to stay the night. Gérard, in retribution, beats her, strips her naked, and leaves her in an abandoned house. Taking Balthazar, he and his friends load the donkey's back with contraband goods which they intend to smuggle across the border. They are shot at by customs officials and escape, but Balthazar, mortally wounded, dies on a hillside among a flock of sheep.
