1955. A boarding school in Belgium. Laurent Matagne (17 years old), thinks he recognizes in his French teacher nicknamed “Vapour”, his father who disappeared during an air raid in 1940. Vapour is eccentric, mysterious, disturbing and brilliant and gives his passion for literature so strongly that Matagne wants to become a writer. Matagne and his friend Boulette decide to hold an investigation. As they build a plot in order to confound Vapour, Matagne devises at the same time his first novel.