The fourth and final story arc of the series is an adaptation of the sixth Oz book, "The Emerald City of Oz" (1910). Continuing on directly from the last story arc, the Nome King is now planning his revenge. Meanwhile, Dorothy is still in Oz. She and Scarecrow has been busy chasing Ozma around the Emerald City, which takes them into a Secret Chamber. Even in the darkness, Ozma discovers a door which reveals to them the Heart of the Emerald City and the history of Oz, proving to Ozma that she must prepare a coronation to be Queen of Oz. Back at the underground kingdom of the Nomes, an Invasion specialist named Guph suggests that in order to conquer the Emerald City they must make a tunnel which will take them to the Emerald City. Along with Guph's Giant Dirt-Devouring Worm, the Nomes make the tunnel and pass underneath the 'Deadly' Desert.