This is the book that started it all - the authors claimed Dan Brown's Da Vinci Code stole their ideas and it is easy to see why. I knew someone who worked with one of the authors, Henry Lincoln, and they certainly believed what they were investigating had a reality. I give this three stars because in the end there is no effective conclusion. It remains a speculation and the secret society of Sion has (as far as I understand it) been debunked as an idea. It remains the best of what has become a small industry of books about secret Christianity usually set in France of Scotland.