How much of Dan Brown's "The Da Vinci Code" do you believe?

Dan Brown author of "The Da Vinci Code" tells a story of a protection of the royal treasure that is protected through the centries known as the knights Templer. In my beliefs I believe there was a relationship between Mary and Jesus and there could of posably been a good chance that she had Jesus child. Do you believe this could of happen? Do you believe he used all the right sources to prove this?