Isle of View (Xanth, #13)

Perplexed Prince Dolph, Xanth's precocious shapeshifter, should be in love but isn't. Nonetheless, he must choose between two fiancees--Nada the uninterested and Electra the uninteresting--or all three of them will suffer the most dire consequences. Luckily a convenient catastrophe has popped up to distract Dolph from his dilemma--the foal-napping of young Che Centaur by goblins. And the only one who knows where Che is is a nice but remarkably naive elflike girl named Jenny from the World of Two Moons. If anyone can save the missing centaur...she sure can't.