Dorothy Gale is gladly joining her Uncle Henry in California to visit relatives who live at Hugson's Ranch, after their vacation from Australia in Ozma of Oz. Dorothy meets Hugson's nephew who is her second cousin, Zeb of Hugson's Ranch. Dorothy, Eureka (her cat) and Zeb are riding a buggy being pulled by a cab-horse named Jim when a violent earthquake strikes. A crevice opens in the ground beneath them and they fall deep into the Earth.