The Wishing Horse of Oz - Ruth Plumly Thompson

Magic wishing emeralds mysteriously arrive in the little kingdom of Skampavia. King Skamperoo immediately confiscates them and wishes to become the Emperor of Oz, with his magic horse Chalk as his advisor. All the residents of Oz are enchanted to forget Ozma and their own rulers, except for Dorothy and Pigasus the flying pig. Can Dorothy and Pigasus break the enchantment and rescue Princess Ozma? Will they forge an unlikely alliance with the Gnome King? And who is the real owner and possessor of the secret of the wishing emeralds?

The Wishing Horse of Oz is the twenty-ninth in the series of Oz books created by L. Frank Baum. (Summary by Beth Thomas)