I've never written a sequel before, and am now deep into book 2 of a proposed chapter book series. It's interesting, trying to balance the old conflicts and background already established with the new material, and to make the book stand alone. The art of the deft "filling in" so the reader does not have to be aware that they missed anything if they are reading books out of sequence, but still have the sense that the characters have a history.
I was disappointed then reading the second book in Hilari Bell's Knight and Rogue series. The first, The Last Knight, was a terrific YA (young adult) read. It had direction and dimension in spades. The second seems to pick up as a true sequel, with a lot of unfinished business from the first book. That didn't bother me with the Percy Jackson series, so much.
No doubt there's a difference between true sequels, like Bell's, or Rowling's, and a series in which the books can more easily be read out of order? I think of our public library and their back wall of elementary chapter books. Some serieses have 19 books in them, so far. Some (Magic Treehouse) have passed 40. If they were written to be read in order... it wouldn't happen!
What are your thoughts on sequels?
3 days ago