Crystal Keepers Five Kingdoms Book

The Five Kingdoms series continues in the third installment, Crystal Keepers. In this book, Cole Randolph and his friends seek to rescue his friends from slavery and free the Outskirts from the clutches of the High King. The team has to traverse various kingdoms, including the futuristic world of Zeropolis that is filled with robots and humans. Cole has to overcome numerous obstacles, including treacherous terrains, villains and dubious allies, to achieve his goals.