Warning: Rants likely for at least 5 paragraphs

The fuss over the da Vinci code seems to have overshadowed the fact that the Mona Lisa is involved in a much older, much more important conspiracy. There was a plot to prevent the formation of all life on Earth using money from the black market sale of that masterpiece and six others just like it painted by Leonardo himself. If anyone can tell me how that was and/or how it was prevented they win a prize... There's a (admittedly somewhat obscure[?] clue beneath.)

-Duggan! What are you doing?! That's a Louis XIV!
-But you're not just going to-
-Just behave like a civilised guest. Now, Herman, if you'd be good enough to show us to our cellar...