The Royal Book of Oz (1921) is the fifteenth in the series of Oz books, and the first to be written by Ruth Plumly Thompson after L. Frank Baum's death. Although Baum was credited as the author, it was written entirely by Thompson. The Scarecrow is upset when Professor Wogglebug tells him that he has no family, so he goes to where Dorothy Gale found him to trace his "roots." Then he vanishes from the face of Oz. Dorothy and the Cowardly Lion mount a search for their friend, but when that is successful, they will need to become a rescue party!