Book excerpt: MONA LISAS GHOST, a thrilling mystery, is the sequel to The Crystal Navigator in the Lucy Nightingale adventure series. During a class video about the Mona Lisa, Lucy and her best friend, Sam Winter notice that the painting seems to be melting. The painting is mysteriously stolen and Lucy must find it before it is destroyed. In an adventure that takes Lucy through the ghost-infested Catacombs of Paris, down underground rivers, and back to sixteenth-century France, she solves a mystery that would shock the world if it were ever made public.