This was the book that got me started on the paleo diet back in 2011.
Robb Wolf is a key figure in the paleo community, and his book provides a solid introduction to the rationale behind the classical paleo diet: no grains, legumes, or dairy. If that's what you're looking for, this book will fill the need.
I don't adhere to a paleo diet anymore because I no longer agree with the scientific justification provided for it. In particular, there's no indication that “leaky gut” occurs to any relevant degree in the general population, whether from gluten or otherwise. Anti-nutritional factors such as enzyme inhibitors and phytates exert only small effects in the context of an overall varied diet. And the carbohydrate-insulin model of obesity fails to account for the observation that many traditional populations remain thin on high-carbohydrate diets.