Marion is a schoolboy in 1840s France who prides himself on strict adherence to a self-defined "rationalism," using it to dismiss emotional displays and avoid affection, earning him the reputation as the "king of cool" among peers. His detachment stems partly from his mother prioritizing her new husband, leaving him alone at school during summer. His self-proclaimed rationalism thinly veils significant emotional immaturity, starkly revealed when he becomes romantically involved with an older courtesan. This affair forces him to confront repressed desires for intimacy and challenges his constructed persona, serving as a catalyst for emotional development and revealing his rationalism as a shield against vulnerability. Marion navigates complex social dynamics among friends, mediating conflicts like a duel between two boys over a girl who actually favors him, and witnessing expressions of unrequited homosexual desire within his peer group. To assert boldness and maintain his image, he participates in dangerous dares, such as a chicken competition standing on railroad tracks awaiting an oncoming train. His summer experiences, particularly the intense affair with the older woman, compel him to reevaluate his understanding of relationships and his own emotions, teaching him the painful cost of emotional naivety and moving him beyond intellectual detachment toward a more integrated grasp of human connection.