My book club kids read Ron Roy's The Absent Author this month, and after discussing the story, we had a few different activities:
Write your own story. Since the book is about an author, it was easy to set out printer paper and construction paper and let the kids make their own books.
Write to the author. We have written to authors during storytime before, so this was a chance for the kids to write to an author of a chapter book instead of a picture book. I noticed that many of the kids chose to write a letter instead of drawing a picture for the author, and yes, I did mail the letters. We'll see if he writes back.
Puzzles. Mysteries are like puzzles, and there aren't many good mystery games for young kids, so I set out a small tabletop puzzle and a floor puzzle with extra-large pieces for them to put together. I watched a group of kids put the floor puzzle together, look at it for a minute, then take it apart and mix up the pieces and try again.
I Spy. This was a way to involve the parents who were at book club and also to use some of our old die cuts we had sitting around in our craft closet. I pinned the die cuts to the wall and left them up as an I Spy game. The nice part about this was that there was no instruction needed - all of the kids had played I Spy before.