"O" is a farm girl from a medieval town just east of one of the great ivory walls that divide the lands of her world. "Chi" is the son of hunters and her best friend. Ob Harpist is a magician from a foreign land. Despite the warnings passed down through generations, the two young people accept the magician's proposition and join him in his travels beyond the wall. Those that guard the walls punish actions such as this by death, but they miraculously survive. The soldiers of the walls hunt them, but they continue to escape. What begins as an adventure toward the edge of the world changes as they begin to learn that the law of the walls is not as simple as they had thought, nor are its enforcers or the world itself. All of their old beliefs are shattered, they are hardened, and they discover their purpose.