L. Frank Baum 
Rinkitink in Oz 

When an island kingdom in the Land of Oz is attacked, King Rinkitink will need help from Dorothy and the Wizard to put things right.With his talking goat, Bilbil, by his side, jolly King Rinkitink of Gilgad sails to the island of Pingaree, where he charms the royal family with merriment and song. But when the festive holiday is cut short by a surprise attack, only King Rinkitink, Bilbil, and young Prince Inga manage to escape capture. After locating the magical Pearls of Pingaree, which give their possessors strength, invulnerability, and wisdom, the three friends set out on a voyage to the terrible islands of Regos and Coregos. But while enemy armies are no match for the combined powers of the three pearls, Rinkitink, Bilbil, and Inga face grave danger when two are lost. When Dorothy Gale and the Wizard of Oz hear of these events, will they be able to act in time to save the day?