Arthur and the Minimoys - Book 1, Luc Besson

Arthur has a lot of worries. A wicked developer dreams of seizing his grandmother's beautiful house where he spends his holidays. There's no question of relying on his parents, who unceremoniously dropped him off there. Nor is there any question of waiting for his grandfather, who mysteriously disappeared four years ago. And to top it all off, Arthur is only ten years old... Perhaps he can count on Alfred, his big dog who is more affectionate than intelligent? Unless, in his grandfather's old library, a grimoire allows him to cross over to the land of the Minimoys. Only they can still save everything!