While not required reading to complete the series, Rain and Fire is an interesting guide book which gives lots of information about all characters and event pre Fire World. It includes art of some animal and dragon characters as well as a few never-before-seen stories. Chris D'Lacey also recounts a lot of memories which inspired events and has many cover artworks which were to be The Fire Within covers and even includes a scrapped sketch of the Dark Fire cover. A must-read if you'd enjoyed the books.