The Devil's Own Crayons by Theresa Monsour

The most famous ceiling on the planet – that of the Sistine Chapel – is bleeding. Oozing through Michelangelo’s masterpiece are hidden pictures predicting disasters or miracles. The world’s leaders assemble a team of three international experts to uncover what the latest shadow painting is foretelling, and the trio soon uncovers the case of three American girls who can cure or kill with the scribble of a crayon.