un-The book

Claire is carrying a book when she flees tucson, a book that belonged to her grandmother and her grandmother's ashes. The ashes are what lead her all the way back to Budapest. The book I don't quite have a handle on yet.

What is the book? Is it a lost tome of some secret knowledge? Secrets of magic? A map to the 22 characters of the tarot? The man in black's guide to power? The trickster/pan/devil's practical joke? A children's book that tells the story of the Pree sisters/family and mirrors the novel?