The third book in the Enchanted Forest Chronicles, if you start with Talking (which really works best.)
This one is told from the point of view of Mendanbar, King of the Enchanted Forest. I'm afraid that my initial impression of him was Another Royal Who Doesn't Do His Duty, because his opening scene is of his refusal to do anything that his steward is complaining about his not doing.
However, things pick up when he finds a section of the Enchanted Forest has been ruined. And there are dragon scales in the waste. A talking squirrel sends him to Morwen, who finds that there was trickery and magic involved. She sends him off to the King of the Dragons, where he finds our princess Cimorene, currently going by the title Cook and Librarian, reasonably hospitable once she realizes he's not out to rescue her, and learns the king has vanished.
They make more discoveries, and Mendanbar insists on coming with her, because she intends to go through the forest, and if anything happened to her, the consequences would be dire.
Their adventures include a flying carpet with teddy bears on it, a spell to keep paint looking fresh and new, a sword that leaks magic, trees springing up where they don't belong, discoveries about staffs, a wicked uncle who doesn't want to abandon his nephew in the forest, and much more.
Light and frothy and fun.