Prince Pompadore and Kabumpo the Elegant Elephant from Pumperdink have to save Oz from Ruggedo the Gnome King, who has run off with the Emerald City to the land of Ev, which is impaled on his head. Wag, a giant rabbit, and a wooden doll named Peg Amy help out.
This is the 1922 book in which Ruth Plumly Thompson adds a G to the Nome King's name.