Dorothy and the Wizard in Oz is the fourth book of the series. An earthquake splits open the earth under Dorothy, and she, her kitten Eureka, her cousin Zeb, and a horse named Jim fall into a city of glass. They are joined by the Wizard of Oz and nine piglets, and must wander through dangerous lands trying to find their way home.

In their journeys, they must cope with invisible bears, flying gargoyles, and a den of young dragons. But rescue, and a return to the Emerald City, are not the end of Dorothy's troubles.