Ruth Plumly Thompson - Silver Princess in Oz

Young King Randy of Regalia is visited by his old friend, Kabumpo, the Elegant Elephant of Pumperdink. Together, they set out to visit their friend Jinnicky the Red Jinn in the Land of Ev. On the way, they meet Planetty, the silver Princess from Anuther Planet, and her fire-breathing thunder colt. When they reach Jinnicky's palace, they find that Jinnicky has been deposed and enchanted by an untrustworthy slave! Can Randy and Kabumpo defeat Gludwig and restore peace and justice to Ev?
The Silver Princess in Oz (1938) is the thirty-second of the Oz books created by L. Frank Baum and his successors, and the eighteenth written by Ruth Plumly Thompson. — Summary by Beth Thomas and Wikipedia