"The world is made of floors linked together by stairs. The floors are made up of rooms linked together by corridors. And when you put together all the floors, you have the world". Such is the theory elaborated by Toto, friend and second head of Siamese twin of a child whose mother has locked away in the huge family manor, where he has been walled-in since birth. Between exploring the endless corridors, private lessons and visits to their father's mausoleum, the brothers have never questioned the limits of this World. Until the day when, obsessed by a strange light they accidentally glimpsed at, they swear to find its end.