Little is known about the upcoming book. Horowitz stated in an interview that the book will indeed be the last of the series and that not all of the Five Gatekeepers will make it, (leaving a hint of one of them dying even though Horowitz dislikes writing about children dying) and at least one will betray the others. He also stated that the book will be separated into five parts, Earth (Matt), Fire (Pedro), Air (Scarlett), Water (Jamie), and Ice (Scott) where the last battle will be placed in Antarctica. Horowitz also stated that he is trying to make a two hundred thousand word book that could take "years to write". We also know that the book will begin with each main character at a different area around the world.