Here is a very small nutshell:
The author holds that Jesus was married to (I think) Mary Madgalene, who was exiled to (I think again) France where she raised their child. It supposes that DaVinci was a part of some secret society that knew about and protected such a "discovery". It also purports inaccuracies of the bible primarily through books like those in the Apochrypha and others that are not included in the more accepted texts.