Like all children his age, Arthur is fascinated by the stories his grandmother tells him before he goes to sleep: his dreams are full of African tribes and incredible adventures, all taken from a book of magic, a souvenir from his grandfather who mysteriously disappeared four years earlier.
When looking more closely at the precious book, Arthur notices that his grandfather has left numerous clues suggesting that a treasure is hidden in the garden. Even more incredible, it would seem that a world invisible to the naked eye lurks underground, a world full of tiny beings called the Invisibles.
Arthur, all of ten years old, is determined to follow his grandfather’s tracks to go over to this other world, the world of the Invisibles, and to discover the seven earths that make up their kingdom. But to enter this domain, there’s but one solution: to shrink and become an Invisible.