To my layman's perspective it seems odd that someone who wrote a book that is "non-fiction" would get all that upset to see that their radical rewriting of history was being adopted and adapted into a best-selling novel and, potentially, a hit movie. Yet, that's the basis of the lawsuit against Da Vinci Code author Dan Brown by Holy Blood/Holy Grail authors Michael Baigent and Richard Leigh.
I've read both books and there seems little doubt that Brown borrowed heavily from Baigent & Leigh's book. (Interesting that the third member of their team, Henry Lincoln, doesn't seem to be involved in the law suit.) Still, weren't they just setting the record straight? I suspect that they're just raging with envy because Brown had the good sense to take their work of 'history' and turn it into a big money maker as fiction.