Lyman Frank Baum 
The Emerald City of Oz (Annotated) 

Dorothy has decided to take Uncle Henry and Aunt Em to live in the Land of Oz, with the help of Princess Ozma. As they embark together on a tour of the land, Dorothy is unaware that the Nome King, squatting in his underground Kingdom, is plotting to seize the Land of Oz. He sets out to recruit new allies to help the Nome army and burrows his way to the center of the Emerald City. Can his diabolical army be defeated by Dorothy, Princess Ozma of Oz, and their friends? In this captivating installment in the Oz series, as well as being reacquainted with favourite characters from previous books such as the Cowardly Lion…