When the last Harry Potter book came out, most passionate fans thought they’d spend years grappling with what to do with themselves without new Potter stories to look forward to. The opposite turned out to be true. Instead, Rowling wouldn’t stop adding to her universe, confronting some fans with a different challenge. On message boards and videos, in fan art and fan fiction, they had taken the world she had created and made it their own. As the author revealed new details about her characters, they had to reconcile Rowling’s vision with their imaginations.