Pierre (Hardy Krüger) is a French Indochina War veteran who is consumed by guilt after having accidentally killed an innocent Vietnamese child when crash-landing his stricken plane. His nurse-girlfriend Madeleine (Nicole Courcel) lives with him on a low-key but potentially romantic basis. Pierre then sees Cybèle (Patricia Gozzi) in distress as she is being dropped off at a small orphanage by an obviously unloving father. Eventually, he pretends to be the girl's father, which allows her to get away from the locked orphanage, and he spends time with her every Sunday, for months. Both are lonely, childlike, and in need of a supportive friend.
A doctor, who has a romantic interest in the nurse, finds out about the ongoing relationship, and out of self-interest interprets Pierre's relationship with Cybèle as sexual. He passes his imagined conclusions on to the police, who also misread the intentions of the young man.
Pierre has nothing to give Cybèle for Christmas, so he takes up her earlier joking challenge to bring her the metal rooster on top of a Gothic church near the orphanage. Being a former pilot, he musters the nerve to climb the 300 foot steeple, and uses his knife as a tool to unscrew and bring down the rooster. He approaches the girl, carrying the metal rooster and his knife. However, at this point, the police arrive and shoot him dead to "protect" the child, whom they think is in danger.
Cybèle, who had fallen asleep waiting to meet Pierre for their Christmas together in the snow covered park's gazebo, is devastated by witnessing the pointless killing of her friend.