Since The Chronicles of Narnia were first written by C. S. Lewis in the late 1940's and early 1950's various schemes of thematic unity have been suggested for the books.  Some have maintained that each of the books represent one of the seven Catholic sacraments.  Others have put forward that each book acts as a commentary on one of the seven deadly sins, or one of the seven virtues.  More recently it has been suggested that each of the seven Narnia chronicles corresponds to one of the seven planets of the medieval cosmos.  But what did Lewis himself say about the overarching and unifying thematic structure of the Narnia books?  That is what this book seeks to set out and explore: what C. S. Lewis called "the hidden story" of Narnia.