Thankfully, this 4th installation in the 39 Clues series was an improvement over the 3rd book which I wasn't crazy about. This book is more like the first two: history, globetrotting, adventure. I enjoyed the focus on Grace and what she had done for Amy & Dan. I also liked the addition of Theo and Hilary & wonder if they will be continuing characters. The lack of Ian and Natalie Kabra did not hurt the story in my opinion either. Sometimes the kids are doing something on their own and I wondered, "ok, where did all the adults go again?" But, it's a kids book. It's not the most well written piece of literature and kids show capability for doing things that "real" kids don't do. I guess that's the point though and what makes it interesting. The pace of 1 clue per book is certainly going to have to increase at some point before getting to book 10 and I still wonder if the "philosopher's stone" will really be worth it, but for now I'm going to keep reading.