I have not read The Da Vinci Code but for the record here is the English High Court decision in
Michael Baigent and Richard Leigh v The Random House Group Limited.

The claim was that the author of DVC infringed the copyright of the plaintiffs who wrote The Holy Blood and The Holy Grail. There was no allegation of textual copying, but copying of "central themes". It was a case of applying the facts to settled law.

The trial judge summarised the law:

an author has no copyright in his facts nor in his ideas but only in his original expression of such facts or ideas…

In other words the facts and the themes and the ideas cannot be protected but how those facts, themes and ideas are put together (this is the Claimants’ "architecture" argument)
can be. It follows from this that the Claimants must show that there is a putting together of facts, themes and ideas by them as a result of their efforts and it is that which Mr Brown has copied. I should say on
passing that there is no claim based on collocation.

Ultimately the judge rejected the plaintiffs’ evidence although he was sceptical about elements of Brown’s evidence.