I didn't think it could be done, but we finally found it: a chapter book my son and I both enjoyed equally. It wasn't too scary for him (at least not once it became clear that Stanley really was going to be able to dig that first hole -- B was super worried about him), and it wasn't too tedious for me. We both looked forward to reading it together, and even made excuses to read longer than usual each evening because we were enjoying it so much. 
 I enjoyed watching my son piece together past and present, watching his jaw drop as he realized the way the characters' families and histories were interconnected. It's a surprisingly sophisticated narrative for a book aimed so young, and it really got him thinking about history, consequences, coincidences, and the bonds that tie us all together. 
 Obviously, if you're an adult you pretty much see it coming, but it's still so much fun to watch a kid work things out and be amazed. Watching my son THINK is just about my favourite part of parenting.