According to cinematographer Axel Cosnefroy, Nicolas Bary wanted the look of the film to be similar to the works of Tim Burton and Guillermo del Toro, as well as settings that could lend themselves to a cartoonish atmosphere.
Nicolas Bary first read Henry Winterfeld's source novel when he was nine years old, and had since been obsessed with adapting it for the big screen.
Nicolas Bary's first directorial effort, the 10000 euro, 10 minute-long short film Before... (2003) was already inspired by Henry Winterfeld's novel, and even already featured Armelle in the role of Corbac, the school teacher.
Nicolas Bary and producer/friend Dimitri Rassam (who's already produced Bary's third short Judas (2006)) spent no less than four years working on this film, from acquiring the film rights from Henry Winterfeld's heirs to the actual filming.
Nicolas Bary had already written a first draft of the screenplay when he met producer Dimitri Rassam, however it was deemed unsatisfactory, even by Bary himself. Nicolas Peufaillit was then hired and endeavored to distance himself from the book and modernize its characters, as he doesn't believe in straight literary adaptations. Thus, Bary and Peufaillit spent 18 months working together on the script, seeing each other every two or three days, acting out the scenes between themselves, creating new characters such as Mireille and Oscar's two bodyguards, injecting emotion and humor, and developing the bad guys.