That would be false. There are historians who, in an academic setting, will argue for the part of the plot about Mary Magdeleine and the child. There are also historians who will argue for the secret society hiding the grail. The truly fictional part is the story of the detectives, the code, and the chase, etc.

I think the whole uproar is the result of a bunch of Christians who don't want other plausible ideas to be presented to the public.