Rinkitink in Oz (Oz Series, Book 10)

Rinkitink in Oz is the tenth book in the Oz series written by L. Frank Baum. It was published on June 20, 1916. It is notable that most of the action takes place outside of Oz, and no character from Oz appears in the novel until its climax; this is due to Baum's having originally written most of the book as a fantasy novel unrelated to his Oz books over ten years earlier, in 1905.
Prince Inga is the son of King Kitticut and Queen Garee, who rule the island kingdom of Pingaree. Kitticut tells Inga that years earlier, when armies from the neighboring islands of Regos and Coregos attempted to invade and conquer Pingaree, they were repelled by Kitticut himself with the aid of three magic pearls. The blue pearl gives its bearer superhuman strength, the pink pearl protects him from any harm, and the white pearl speaks words of wisdom.