It's old hat for novelists to be sued for reusing plot points and characters from earlier fictional work. Sometimes it's old work -- as when the estate of Margaret Harris sued the author of a parody of Gone With the Wind, only to have the courts reaffirm for the umpteenth time that parody is fair use. Sometimes it's movies, or TV sitcom concepts. And every once in a blue moon, there's a book which is successful enough to attract this kind of attention.
Well, here's a new variation on the theme. The target is Dan Brown's "The Da Vinci Code", a book which didn't impress me at all. (If you want thought provoking historical fiction on the origins of Christianity, go read "The Dream of Scipio" by Iain Pears; if your tastes run more to religiously themed potboilers featuring secret histories of the church and supernatural fireworks, try The Apocalypse Door by James Macdonald). But it sure did make a whole lot of money. As a result of which, the authors of "Holy Blood, Holy Grail", an earlier book which similarly had the early Christian church hiding the marriage of Jesus.
But what's new here is that "Holy Blood, Holy Grail" was at least presented not as fiction, but as the result of its' authors research into actual fact. And, at least judging from the initial press account, there isn't yet any allegation that the text of Brown's novel was cadged from "Holy Blood" (which is what got a whole bunch of historians in trouble not too long ago). What Brown's supposed to have stolen is plot points and characters. The plot points are the "facts" that the research supposedly uncovered. The characters are the authors of "Holy Blood, Holy Grail", who were stunned and dismayed to discover that the new book's characters include people who spent large chunks of their lives researching the history of the early church -- just like them. Next up: the descendants of Huey Long sue the estate of Robert Penn Warren to get what's theirs for "All the King's Men."
Now, the usual rationale for these sorts of lawsuits is that the plot is the first author's original work. But it was reported in their own book as fact, not as something that they had made up. If they'd like to change their minds about that, I'm sure that there will be interest well beyond the courts.
To sum up, these folks believe two things. First, there is strong evidence that the early church covered up important events in the life of Jesus. And secondly, that anyone who talks about it has stolen their work, and owes them money. I guess we'll see soon if the courts in New Zealand let you assert copyright on a (purported) fact.