Professor Wogglebug gets the characters of Oz thinking about their genealogy and where they came from because he wants to write The Royal Book of Oz recording all this information. This topic especially upsets the Scarecrow, as he knows that he was discovered by Dorothy hanging from a beanpole in a cornfield and he thinks that this mean he can't possibly have a family history. Woggleburg agrees and hurts Scarecrow's feelings by noting that because of Dorothy's discovery, Scarecrow has no family tree and should get the slightest mention in their Royal Book of Oz.
Scarecrow decides to go on an adventure to find out more about his past and ventures down below Oz to learn more. He winds up in the Land of the Silver Islands, whose people resemble the Chinese and who greet him with cheers welcoming back the Emperor. Scarecrow then begins learning about his unknown past life and his importance among the the people of the Silver Islands. While Scarecrow is away, Dorothy notices his absence and embarks on her own adventures to find him. United at last, they must work together to return to Oz.
L. Frank Baum (1856-1919) was an American author of children's books, most famous for his The Wonderful Wizard of Oz. Baum wrote 13 sequels to his first Oz book and still has a huge fan base to this day. The Royal Book of Oz was the first book posthumously attributed to Baum, and was actually written by Ruth Plumly Thompson. It is the 15th book in the Oz series.