In the picturesque French countryside, close to the majestic Pyrenees, a young donkey finds itself adopted by the adventurous children, Jacques and his sisters, who reside on a quaint farm. They lovingly name the donkey Balthazar, with the help of Marie, Jacques's childhood love, whose father teaches at the nearby school. Tragedy strikes when one of Jacques's sisters passes away, prompting their family to leave the farm, which is then taken over by Marie's family in a somewhat informal arrangement. Unfortunately, Balthazar ends up in the hands of local farm workers who subject him to relentless toil.
As the years roll by, a mishap sends Balthazar fleeing back to Marie, who has grown into a young woman. However, discord brews between their families as Marie's father becomes embroiled in legal disputes with Jacques's father over the farm, leading to Balthazar being given away to a local bakery for deliveries. Among those at the bakery is Gérard, the leader of a youthful criminal gang who feels a pang of jealousy towards Balthazar because of Marie's affection for the donkey. Under Gérard's cruel management, Balthazar's suffering intensifies.
One fateful day, while driving her 2CV, Marie spots Balthazar by the roadside and stops to reconnect. Yet, Gérard, having been resting nearby, insists on joining her in the car, which leads to a harrowing implication of a sexual assault. This dark encounter marks the beginning of Marie's tumultuous and abusive relationship with Gérard, culminating in her estrangement from her family. In a tense turn of events, Gérard finds himself questioned by the police alongside Arnold, a local alcoholic also entwined in a murder investigation, but neither is apprehended.
As Balthazar falls ill and is at risk of euthanasia, Arnold intervenes, taking the donkey under his care. Balthazar rebounds and starts guiding tourists through the stunning Pyrenees with Arnold's help. However, his spirit remains restless, leading him to escape and join a circus. When he spots Arnold in the crowd during a show, his instinctual loyalty drives him to chaos, prompting Arnold to reclaim him. As fate would have it, Arnold inherits a fortune after the death of his uncle and throws a celebratory party. Meanwhile, Marie and her mother have a heart-to-heart, but Marie resolutely refuses to return home.
Tragedy strikes again when Gérard forces Arnold to ride Balthazar in his drunken state, resulting in a fatal accident. Subsequently, the police send Balthazar to the market where he is purchased by a greedy local miller who mistreats him for labor. One stormy night, Marie, drenched and desperate, pleads for refuge at the miller's door, having fled from Gérard. The miller offers help, posing as a compassionate ally, but the next morning surprises Marie by inviting her parents and offering them the donkey—an implication that she might return to her troubled home life. Torn between her feelings for Jacques, who wishes to marry her, and her traumatic past with Gérard, Marie faces an emotional dilemma.
One day, determined to confront Gérard, she seeks out the barn that holds bittersweet memories. However, she falls into a trap set by Gérard and his gang, enduring a brutal assault before being rescued by her father and Jacques, who hastily take her home with Balthazar's help. In a shocking twist, after her father dies—which follows a visit from a priest—Gérard pressures Marie's grieving mother into yielding Balthazar for use in his criminal endeavors.
In the dead of night, Gérard steals Balthazar for smuggling operations across the Spanish border. When the plan goes awry, resulting in a violent confrontation with custom guards, Balthazar is left to meet a tragic fate. In a poignant scene the next day, the once valiant donkey lies down, succumbing to its wounds as a flock of sheep gathers around him, their bells tinkling softly, marking the somber end of Balthazar's journey.
