For only the fourth time in two centuries, the French have allowed the Mona Lisa to leave the Louvre, this time at the request of the pope, who wants to exhibit it in the Vatican Museums. However, once on display, the Museums' former curator notices a nearly imperceptible discrepancy in the painting, leading to the discovery that it's a forgery. Faced with the crisis of losing the most valuable painting in the world, the pope turns to Mauro Bruno...