Rinkitink in Oz
Prince Inga of Pinagree, the future king, has been entrusted by his father, the King, to keep the secret of the three pearls. These pearls give their bearer magical powers. Then one day, Kink Rinkiting comes to visit the small island country with many presents for the Royal Family. While he is staying there, a band of barbarians from another island invade the country of Pinagree. The king tries to get the pearls, but is not fast enough and is captured. However, Inga and King Rinkitink are able to escape and Inga is able to find the pearls. Through their advice, he is able to set off on a journey to rescue his parents, which eventually brings him to Oz.
You can buy this book through the Emerald City of Oz from the following publishers: