When Enrique Ardiach, an important businessman and well-known antiquarian, dies in a strange plane accident, his two grandchildren Elisabet and Eduardo are left on their own. They find their grandfather's briefcase in the wreckage of the plane, along with mystical signs and a hastily scribbled note telling them to "look for Gerard de Villiers". Elisabet and Eduardo undertake the search for de Villiers, and for the Book of Thot, recognised as the first book in history, whose pages are said to contain all human knowledge. However, they are not alone: there are also the custodians, whose task is to save and study banned books; the men in black, who want to destroy them and the Catholic Church, which wants to keep them hidden. Elisabet and Eduardo will encounter strange and sinister people, come face to face with the supernatural and travel all over Spain in their search.