We find Lucky Luke in his youth, fast with stone lance and mounted on a small white horse with the yellow mane, already. Old Timer, whom he accompanies, intimates to him the order to stay at the school of Mushroom City, the time for him to settle (at the saloon) some things. Luke does not like it, but he ends up obeying. Detesting to learn alone, he ramutes (of course or force) all the school-age youth of the village, including the Dalton brothers. And the life of the school goes quietly until the arrival of a new student, older, answering the name of Oklahoma Jim. And all his purposes are not well pure, even manipulators...