During a class video about Leonardo da Vinci, Lucy Nightingale and her best friend, Sam Winter, see something terrible happening inside the Mona Lisa. A purple storm engulfs the once sunny landscape, lightning rips the sky, and letters float in Lisa’s left eye. Sam believes that a molecule-destroying syndrome is destroying the painting. When it mysteriously vanishes from the Louvre, Lucy and Sam embark on a harrowing adventure that takes her into the phantom-infested catacombs under Paris, through unexplored rivers deep within the earth, and back in time to ask Leonardo da Vinci for an important favor. This is a mystery that would stun the world if the facts were made public.