While travelling the world with their parents, Carter and Eli Hayes learn of a Hidden World and together they must solve the clues to uncover the treasure. When Carter and Eli Hayes discover an old letter in their great-grandmother's attic, they embark on an icy adventure in search of the Hidden World. With dangers at every turn, the boys must use their wits to solve the riddles and return home safely. But, with the harsh Arctic landscape, will they succeed in their quest or be left out in the cold? While reading these books, kids will explore the world through imagination and learn about various countries. The central theme of brotherly love will prevail as Carter and Eli work together, face their fears, and overcome sinister forces competing against them. If your child enjoys travel and adventure, this is the series for them. Book 2: While vacationing in Greece, Carter and Eli's encounter with a mysterious stranger leads them toward their next adventure. If they are going to find the Hidden World, they must work together to solve the riddle and navigate through dangerous obstacles along the way. But, with sinister forces acting against them, will they succeed in their quest or be left disappointed? Book 3: Following an eventful day at the medina in Marrakesh, Carter and Eli are eager to set off on their next adventure. After sneaking away into the desert, they must work quickly to solve the riddle and find the missing map piece. But, with the clock ticking and evil lurking in the shadows, will they succeed in their quest or run out of time?