Many thinking Christians will already be aware of the part that St Paul and, later, Constantine, had in shaping the religion they know today. This book fills out some historical details which illustrate in an astonishing way the contrast between "gentle Jesus meek and mild" and how much more ruggedly He would have been perceived as The Leader in the context of His time and place. It also proposes that as a Jew it would have been most odd if Jesus had not been married and had children. This unusual slant on Jesus explains in one stroke the many anomalies and inconsistencies in the Gospels as manipulated by Paul and Constantine. This is a challenging section for Christians, but the authors treat your beliefs with utmost respect and assert that what they have come up with is already known to theological students (includes your local priest) and will deepen, rather than wipe out, the beliefs of a serious Christian disciple.
The next section is a cogent, sweeping piece of work which explains the human need for something to believe in, and how 20th century dictatorships stage-managed events to fill those needs. If you ever wondered how a beast like Hitler could charm one of the most civilised peoples on Earth, here is one plausible explanation. Really worth reading, in my opinion.
The last section suggests there is a quasi-secret organisation of aristocratic families who have held "the secret" that Jesus did marry and his bloodline continues today. This society holds an intention that one day the heirs to David's line, through Jesus, will come to rule. It sounds corny in this précis form, but there is hard evidence that this society exists and is both serious and influential.
So, the thread that runs through the book is that Jesus was from the royal lineage of David (undoubtedly true) had children (most probably) and his heirs exist today. I found this argument weakening and running out of steam towards the end, however.
Conspiracy theorists will love it; academics, pedants and fundamentalists will hate it. If you are open-minded, go for it. You will definitely learn a new slant on certain aspects of history.