KNOWLEDGE IS THE KEY is the fifth book in THE LEAF'S KEY SERIES. This spine-tingling page-turning book carries readers off to Skinwalker ranch to face the Lockers and other demons, and to the scariest Island in the world, La Isla de las Munecas. Leaf and Lilly save their friend Apple when she meets a creep on the internet. Leaf bravely saves her friends from a fire but suffers a personal loss. Leaf comforts a friend who is shockingly pregnant. Leaf discovers Pythagoras, Plato, and the magic in maths. Informative Fiction. Leaning has never been so exciting!