Dorothy Gale and her cousin Zeb find themselves falling through a massive fissure in the earth during a violent earthquake, accompanied by their horse Jim and a white kitten named Eureka. They land safely in the transparent, beautifully colored glass city of the Mangaboos, a vegetative race of people who possess no hearts and walk upon the air. Falsely accused of causing the destructive Rain of Stones, they meet the Wizard of Oz, who has also arrived via a runaway balloon. The Wizard defeats the Mangaboo sorcerer in a contest of clever illusions, and Dorothy ultimately picks the royal princess from a bush to restore rightful order.
Escaping the kingdom, the travelers navigate through a dark mountain tunnel into the charming Valley of Voe. Here, invisible inhabitants and unseen bears consume the magical dama-fruit to remain hidden from danger. Using cleverness and the guidance of an unseen friend, they cross the river safely and reach Pyramid Mountain, scaling a spiral staircase that leads to the wooden realm of the Gargoyles. After battling these silent, winged wooden creatures, they manage to fly across the abyss using detached wings and fire-building strategies.
Further underground, they encounter a den of baby dragons guarded by a fierce mother's absence and navigate complex turning-rock puzzles that lead closer to the surface. Though separated from their familiar world, Dorothy relies on her friendship with Princess Ozma, who watches over them through an enchanted picture in the distant Land of Oz. Utilizing the powerful Magic Belt, Ozma summons Dorothy, the Wizard, and their companions to the glorious Emerald City, where they are warmly reunited with old friends like the Scarecrow and the Tin Woodman.
The narrative follows a series of festive celebrations, processions, and a memorable trial in which the kitten Eureka is falsely accused of eating a tiny royal piglet. Eureka's playful trickery is finally exposed when the missing pet is found safe inside a narrow-necked vase, restoring harmony to the royal court. Having experienced the marvels of fairyland and reconnected with familiar faces, Zeb and Jim are finally wished back home to Hugson's Ranch by Ozma's magic, while Dorothy returns safely to her uncle and aunt in Kansas.
