The Mostly Invisible Boy, by AJ Vanderhorst, is a book about how an intriguing boy finds out a secret that the rest of the world has never known about. When Casey Grimes, the main character, finds out that most people thought he was invisible, he thought it was just a joke being played on him by the other kids. Now, he believes them. As he goes around sixth grade, the teacher doesn’t call on him, the other kids don’t notice him, and he never gets detention because no one notices his mistakes. However, his life at home is as normal as any other kid, including his favorite thing being to climb the trees of the forest nearby. But one day, when his parents win a vacation to Jamaica, they leave Casey and his sister, Gloria, with a peculiar lady named Ms. Jones. The babysitter seems to know a lot about everything, and she doesn’t seem surprised when Casey is climbing a tree alone in the forest, and she only tries to find him when it gets dark. In the meantime, Casey had found a particularly gigantic tree, wider than any he had even dreamed of. Once he had circled the tree a couple times, he noticed a ladder made of metal connected to the tree and he decided to try to scale the behemoth. After a long time, he made it to the top to find a platform made of wood, and a large one at that, and he fashioned a note by writing on a kite to send back to Ms. Jones. The next day, Casey decides to bring Gloria with him to the tree and show her the awesome surroundings. They end up finding a new society filled with children who are training for combat. Helped out by a girl named Luciana West, Casey and Gloria try to not get caught, but they also try to figure out what is going on in the foreign country known as the Sylvian Woods.