In the forest the mare Mirabelle has more than one reason to be proud : she's the mother of Pom and the best horse in the team to help the forestry workers. She loves towing the cut trunks with the other horses and the dockers. But then, she's held wrongly responsible for an accident in which the boss's son has got injured. She's sold and separated from her foal. Julien, the old groom, wants to help the young horse, but Porn gives himself over to despair. As a mother, Mirabelle would to anything to be reunited with her son.