Dorothy begins this new adventure into the fairylands of Oz when an earthquake splits the earth open under her. She, her kitten Eureka, her cousin Zeb, and a horse named Jim fall into the hole and land in a city of glass. This land under the earth is home to a cold, heartless vegetable people. Dorothy and her friends are joined by the Wizard of Oz and nine piglets, and then make their way through a series of dangerous lands trying to find their way back to the surface of the earth, and home. They wander through the Valley of Voe, which is inhabited by invisible, deadly bears. Here they learn how to walk on water to escape the bears. They make their way through the inside of a mountain and emerge in a dead and soundless world inhabited by wooden, flying gargoyles. Escaping these menacing creatures, they find themselves in a den of young dragons. Finally, just when it seems they are doomed to die imprisoned in yet another underground cave, Princess Ozma sees their plight and rescues them. Safely back in the Emerald City they renew old friendships, but are interrupted when one of the piglets turns up missing. Dorothy's ill-mannered kitten is accused in the mystery and a murder trial ensues, with the Wogglebug as the prosecutor and the Scarecrow as the defense attorney. But all ends well and Dorothy, Eureka, Zeb, and Jim return to their homes on the earth's surface after this intriguing adventure.