What is the overarching theme?

One of the central themes in the book Inkheart is the astonishing ability shared by Mo and his daughter Meggie to read characters and objects out of books and into real life. For Mo, this begins as a simple exchange of inanimate objects, though he is not at first aware that there is a quid pro quo necessary in the phenomenon, and that for every item that he reads out of a book, an item near by in real life disappears into the story. Mo quickly learns that this miraculous feat can only take place when he is reading aloud.