The 25th Oz book, penned by Ruth Plumly Thompson, published in 1931 by Reilly and Lee with 12 color plates and black-and-white illustrations by John R. Neill.
Peter, the little boy from Philadelphia, Pennsylvania (who twice before has saved Oz from the Gnome King (see The Gnome King of Oz (1927) and Jack Pumpkinhead of Oz (1929)) meeets up with Captain Samuel Salt on his ship, the "Crescent Moon." Along with King Ato, former king of the Octagon Isles and Roger the Read Bird,
they set sail on the Nonestic Ocean, meeting Breakfast the Bananny Goat whose ears are bananas, the Duke of Dork, and Pigasus the Winged Pig whose rider must talk in rhyme.
Meanwhile, Ruggedo, the former Gnome King rendered speechless by the Silence Stone for the past five years, answers an advertisement for the kingdom of Menankypoo, where they can't talk but words run across their foreheads, and becomes their king. He discovers and enters a seaside cave belonging to Kadj the Conjurer. Inside a cabinet marked "Sure Cure for Everything" he finds an axe that cures his speech problem. With Clocker the Clock Man, a speechless wise man giving forth words of wisdom every 15 minutes (via written notes from a cranially implanted cuckoo bird), Ato's former subjects and Salt's former pirates, he sets off to conquer Oz again.
Will Pigasus, Peter, Captain Salt, Roger, and Ato make it to Oz in time to save Queen Ozma, the Magic Belt, and the whole kingdom? (Spoiler: All Oz books have a happy ending, and there are another 15 books after this one.)
This is Peter's last appearance in the Oz books. He says he and his grandfather will return and teach Ozma and the Ozites how to play baseball, but Thompson never followed through on this promise.