The Ghost Forest (Secrets of the Sky, Book Three‪)‬

Kiya and Kinjal return to the Kingdom Beyond.For their next adventure in the Kingdom Beyond, twins Kiya and Kinjal must help the flying horses with a sudden invasion of their lands. It turns out that the tree ghosts are losing their forest! To save the trees, and the Kingdom, they must use their collective knowledge of this world and of course their magic!