1955. A boarding school in Belgium. 17-year-old Laurent Matagne believes that his French teacher nicknamed "Steam," is actually his father, who disappeared during an air raid in 1940. Steam is eccentric, mysterious, troubling, and brilliant, and he quickly communicates his passion for literature to Laurent, to the point of stirring the young man's desire to become a writer. Matagne and his friend Boulette decide to carry out an investigation. When they hatch a plan to trap Steam, Matagne sets about writing his own novel.