The book begins as King Kitticut, who rules the island of Pingaree in the Nonestic Ocean beyond the continent which Oz is the center of, tells his son Prince Inga about the secret defenses of their country. Pingaree was once invaded by the armies of Regos and Coregos, two neighboring islands to the north. The invaders were defeated through the use of three Magic Pearls, gifts of the mermaids. The Blue Pearl gives superhuman strength; the Pink Pearl protects the bearer from all harm; and the White Pearl provides words of guidance that only the bearer can hear. Using these pearls, Kitticut's father and predecessor had led his people in an effective resistance against the invasion; the forces of Regos and Coregos were driven out, and drowned on their journey home. Inga has become old enough to learn these secrets, and Kitticut tells his son of the pearls' secret hiding place.
The next day, Pingaree receives a royal visit from Rinkitink, king of the country of the same name, a plump and jovial neighboring ruler. Rinkitink is accompanied by his surly talking goat Bilbil. A surprise attack from Regos and Coregos lands suddenly, and seizes King Kitticut before he can make use of the magic pearls. The island is devastated and the inhabitants consigned to slavery. Inga evades the enemy by remaining hidden high in a tree, while Rinkitink accidentally falls down a well. Once the island is deserted, Inga rescues the king, finds the goat (who had been ignored by the invaders), and retrieves the pearls. Thus the three of them set out to free the citizens of Pingaree.
The novel derives from a 1905 manuscript which Baum originally wrote as a stand-alone fantasy book, but which was unpublished for unknown reasons. Having been quite busy with his film company and his health issues at the time, he simply tacked on an Oz-related ending and submitted it to the publisher as his yearly, contractually-obliged Oz book. Since that original manuscript no longer exists, it is up for debate whether it had a different ending before it was made into an Oz book or if it had simply been unfinished beforehand. The resulting Deus ex Machina ending due to Dorothy and Ozma's sudden involvement in the plot is surprisingly unpopular with Oz fans, to the point where a legally published Fix Fic, King Rinkitink, was authored by Andrew J. Heller and released in 2017 with the backing of the International Wizard of Oz Club, in an attempt to bring the story back to what the original manuscript may have been like, sans any Oz elements.
- Amplifier Artifact: The three pearls.
- Baleful Polymorph: Bilbil the goat is revealed to have actually been a human prince at the end of the story, with no real lead-up or foreshadowing to this reveal.
- Big Fun: King Rinkitink himself, an overweight but jolly and humorous king.
- Convection Shmonvection: The lava chamber which the Nome King forces Prince Inga to navigate (which may make some modern readers wonder if Baum foresaw the The Legend of Zelda games).
- Deus ex Machina: Dorothy's rescue of the Prince and King Rinkitink, defeating the Nomes with eggs. Some have criticized this as cheapening the struggle the characters have endured up to this point.
- Huge Rider, Tiny Mount: King Rinkitink riding the unfortunately puny Bilbil the goat.
- Intergenerational Friendship: Between young Prince Inga and King Rinkitink.
- Invincibility Power-Up: The Pink Pearl is a literary example. Even arrows and spears miss their mark as long as Pingaree has the pearl on him, like an invisible force field.
- Lord Country: King Rinkitink is the ruler of the country of Rinkitink.
- Made a Slave: The fate of the inhabitants of Pingaree after the invasion.
- Non-Human Sidekick: Bilbl the goat is this for King Rinkitink until it's revealed he was Human All Along.
- Reluctant Ruler: King Rinkitink stays with Prince Inga for so long partly because he'd rather be almost anywhere than in his own kingdom where he has responsibilities.
- Royals Who Actually Do Something: The protagonists are both royals who go through quite the adventure.
- Too Important to Walk: This is the reason King Rinkitink has Bilbil.