Will they solve this medical mystery in time? When Bo Salisbury hurts his ankle playing soccer, doctors think it's a bad bruise. Soon his leg gets worse, and he feels very sick. High-interest topics, real stories, engaging design, and astonishing photos are the building blocks of the XBooks, a new series of books designed to engage and motivate reluctant and enthusiastic readers alike. How can a bite from a pet prairie dog cause a life-threatening illness? Where does the guinea worm, a parasite that lives under human skin, come from? How can a virus that attacks the brain be related to birds dropping dead at the zoo? With topics based in science, these action-packed books will help students unlock the power and pleasure of reading... and always ask for more!