Since the death of his mother, Pascal, ten years old, spends his holidays with his father, the rich Laurent Segur. One day, when diving near the shores of Corse, an aircraft falls into the sea. The holiday goes on happily with Catherine, the young and pretty girlfriend of Laurent. But soon blue marks appear on the face of Pascal. He has been contaminated by a nuclear weapon carried by the destroyed plane, and he won't survive more than six months. There is nothing Laurent can do, except give his son the best six months he has ever lived.

Laurent, a widowed French-American millionaire, and his 10-year-old son, Pascal, are fishing near a desolate Corsican beach when a plane carrying an atomic weapon explodes overhead. Because Laurent is swimming underwater at the time, he suffers no harmful effects, but Pascal is exposed to radiation and develops leukemia. Upon learning that his son has only a few months to live, Laurent stops working and takes Pascal to his country chateau. With the aid of his fiancée, Catherine, an art director for Paris Match, his wartime friend Verdun, who works as a caretaker at the chateau, and Verdun's wife, Marinette, Laurent tries to indulge the child's every whim. It soon becomes apparent that Pascal is aware of his fatal illness and calmly accepts the approach of death. Pascal loves his surroundings, and his father buys him a blue tractor and trailer to drive around the chateau grounds. Because the boy shows an interest in wolves, Laurent and Verdun break into a Paris zoo and steal two of the animals so that Pascal may train them as pets. After one of the wolves is rescued from a fall into a well, the boy nurses the animal. Later, a wild stallion colt attacks Pascal while he plays, and the wolves come to his rescue. On Christmas Eve, while Verdun is dressing for dinner and Laurent and Catherine are out doing last-minute shopping, Pascal begins to weaken. Upon returning to the chateau, Laurent discovers that his son has died at the foot of the Christmas tree, surrounded by his opened presents and guarded by his two howling pet wolves. Pascal's last gift to his father is a hand-carved wooden plaque wishing him and his friends good luck.