By request, I am starting in on the works of the second Royal Historian of Oz, Ruth Plumly Thompson, of which this is the first.
Professor Woggle-Bug takes it into his antennaed head to compose a genealogical tome concerning the principal persons of Oz, beginning with Ozma. He presents the idea to the court, and it met with general favor by everyone except the Scarecrow, who is embarrased that he knows of no ancestors; he sneaks out of the palace and the Emerald City, determined to find his family tree.
(Incidentally, I'm not sure why the Scarecrow would be any more prone to such a perplexity than, say, Tik-Tok or Scraps; but we'll let that alone. It's fantasy.)
Returning to the Munchkin farm where he was created and the very beanpole on which he had been hung to scare the crows, he begins digging for roots...and falls through the earth for a great distance. A _very_ great distance, until, at last, he finds himself (with quite a bump) on what he soon learns are the Silver Islands, and is proclaimed their Emperor. Not, mind you, because he descended from above -- well, that too -- but because he is considered to be their Emperor, Chang Wang Woe, who, as the Grand Chew Chew explains, was by prophecy promised to return to them via that same beanpole.
(Yep. The Silver Islands are a racist version of comic Chinese. Ah, well, Baum did a few rather racist things himself, so we'll let that pass also. We give _The Mikado_ a break, after all; and at least Thompson doesn't have them calling him a Scaleclow or some such nonsense...)
Meanwhile, the Ozites have no idea where their friend has gone. Dorothy and the Cowardly Lion decide to go looking for him, and immediately set out in the wrong direction. After various adventures, they come to city of Pokes, where people are slow, and the land is under a spell of constant sleepiness. Taken prisoner for exceeding the 1/4 mile per hour speed limit, they escape with another prisoner, a gallant knight named Sir Hocus, by singing (which the Pokes simply can't abide).
We return to the Emperor/Scarecrow, who saves the Silver Islands from an invasion by use of a magic fan that creates great winds, and blows the invaders away.
Lots more adventures pass before Dorothy's party meets up (by way of a Wish Road) with the Scarecrow and they all return to Oz just in time for the mandatory Oz party.
It's well-paced, far better so than some of the Oz books from the middle of Baum's run. While the writing is definitely not Baum's, the plot is: Thompson was working with notes Baum had made for a fifteenth Oz novel.
She had been nine years old when _The Wonderful Wizard_ came out, and became one of Baum's main child correspondents. She had sold several short stories to children's magazines while herself a minor, and, by 1918, had written a children's book (_The Perhappsy Chaps_). But it was her work on the children's Sunday page for the Philadelphia Ledger that caught the attention of William F. Lee, vice-president of Baum's publisher, Reilly and Lee; he offered her the job of continuing the Oz series and, when she accepted, provided her with Baum's notes. They were incomplete, and Thompson filled them out to suit herself.
Official Ozstory tells that after publishing this one, she was transported to Oz for a day, where she met Ozma. Ozma explained that Oz books were _not_ to be made up, and gave her a magical phone number which she could use to get the latest Oz news. Thus (it says here) her next book, and those that followed, were much more accurate.
That being the case, I'm looking forward, albeit with some trepidation, to the first Oz book written wholly by Thompson, with the peculiar title _Kabumpo in Oz_.