This is the 10th book in the legendary Oz series, released in 1916 and written by the iconic author, L. Frank Baum. It's worth mentioning that none of the lovely Oz characters appear in this novel right up until the very end, and that's partially explained by the fact that Baum wrote it as a standalone story more than a decade earlier.
Pingaree is a beautiful island right in the heart of the vast Ocean that encircles the majority of the magical countries and lands that, in turn, surround the perilous Deadly Desert (the sand in this desert turns anything into dust) that's all around the glorious Land of Oz. Back in the day, the fierce and brutal armies of the neighboring kingdoms wanted to invade and conquer the island, but Pingaree's valiant king was able to stop their march: he used 3 magic pearls that the Mermaids entrusted him with.
The blue one gave the man supernatural strength, the Pink one turned his body into an impenetrable shield, while the White one was like a never-ending well of knowledge that only he had access to. Thus, the king crushed the invaders, brought his folks victory and peace, and the conquerors left the land in defeat. Rinkitink in Oz follows the adventures of Kitticut, the king's brave son, his wife, and their witty child.
Land of Oz works:
1. The Wonderful Wizard of Oz (1900)
2. The Marvelous Land of Oz (1904)
3. Ozma of Oz (1907)
4. Dorothy and the Wizard in Oz (1908)
5. The Road to Oz (1909)
6. The Emerald City of Oz (1910)
7. The Patchwork Girl of Oz (1913)
8. Tik-Tok of Oz (1914)
9. The Scarecrow of Oz (1915)
10. Rinkitink in Oz (1916)
11. The Lost Princess of Oz (1917)
12. The Tin Woodman of Oz (1918)
13. The Magic of Oz (1919, posthumously published)
14. Glinda of Oz (1920, posthumously published)
Together they're raising a boy, Inga, and he's about to learn of the magical abilities of the pearls. One day, when the kid is old enough, his father tells him where he's hiding them. King Rinkitink, a royal guest, arrives the next day. He's a joyful, plump fella who enjoys the life in Pingaree for a couple of weeks. Soon, a new horde from Regos and Coregos devastates the island - they capture the leader before he can put up a fight and enslave all the inhabitants, except for Inga, the fat king, and his goat.