Social media is all abuzz with the story of J.K. Rowling, author of the Harry Potter books, taking actor Alan Rickman aside and confiding to him a secret. No one else knew what was going to happen in the series, of course, but Rowling knew Rickman needed this piece of information to play his character in the movie adaptation.
So how do the writers of books in a series do it? Plot it all out in advance like Rowling did? Or, as many authors maintain, do the characters take over and surprise their authors?