The Maze of Bones by Rick Riordan is the first book in the 39 Clues series. Meet brother and sister pair Amy and Dan Cahill, whose job is to find a very important clue that their late grandmother, Grace Cahill has left to them in her will. This series is very popular with children, especially those who love adventure books. Read The Maze of Bones and the rest of the 39 Clues series by Rick Riordan et. al.