Can't say enough good things about this series. Written for kids but still a great read for adults on a nostalgia kick.
I thought this was better than #3, but not quite as good as #1 or #2. There was significantly less racism/bigotry in this one (yes, I know, they were written in the 1960's, things were different) and there were more puzzle-type mysteries rather than mysteries that required knowledge of obscure fact...
There was a bit of longing when I read this book. Encyclopedia's father was so patient and caring with him. He helped Encyclopedia learn without hitting him or calling him stupid. I wish I had a father like Encycopedia's.