In a medieval yet futuristic world, Clay, Aaron, Lance, Princess Macy, and Axl are five young knights who protect the kingdom of Knighton and it's capital Knightonia from Jestro, the Book of Monsters, and their army of Lava Monsters.
By the third season, the Cloud of Monstrox appears following his defeat as the Book of Monsters as he once again controls Jestro into helping him obtain the 10 Forbidden Powers where the Cloud of Monstrox uses his evil lightning to animate his Stone Monsters.