When Mallory and Jared attempt to rescue Simon from goblins, they use a magical stone which enables them to see things that are normally invisible.

Holly Black is the author of bestselling contemporary fantasy books for kids and teens. Some of her titles include The Spiderwick Chronicles (with Tony DiTerlizzi), the Modern Faerie Tales series, the Curse Workers series,?Doll Bones, The Coldest Girl in Coldtown, The Darkest Part of the Forest, ?the Magisterium series (with Cassandra Clare), and the Folk of the Air series. She has been a finalist for the Mythopoeic Award, a finalist for an Eisner Award, and the recipient of both an Andre Norton Award and a Newbery Honor. She lives in New England with her husband and son in a house with a secret door. Visit her at BlackHolly.com.Tony DiTerlizzi is a New York Times bestselling author and illustrator who has been creating books with Simon & Schuster for fifteen years. From his fanciful picture books like Jimmy Zangwow’s Out-of-this-World Moon Pie Adventure, Adventure of Meno (with his wife, Angela), and The Spider & The Fly (a Caldecott Honor book), to chapter books like Kenny and The Dragon and The Search for WondLa, Tony always imbues his stories with a rich imagination. His middle grade series, The Spiderwick Chronicles (with Holly Black), has sold millions of copies, been adapted into a feature film, and has been translated in more than thirty countries. You can visit him at DiTerlizzi.com.