They got to go boating when they "borrowed" their grandfather's sailboat. And they got to go swimming when the boat sank off the coast of a tropical island. Now they are going to get to go hiking, because a bizarre genie named Rialti has turned Chealey into a camel and won't turn her back until they bring him a magical dragon's horn from the other side of the Crown of Amaranth.

For the protection of the magical people and animals that live in the Crown of Amaranth, its exact location must remain secret. It is one of the last refuges of giants, trolls, witches, unicorns, fairy folk, and dragons, all of whom have their own reasons for delaying the children in their quest.