Del Ryder and the Battle for Azdia - Del Ryder, #4

Darkness has fallen across all of Azdia. Soon, all of life will stop glowing with light. The tress have lost their life. Even the mighty feldroes have ceased to roam freely. Most of the lumens, the shape-shifting caretakers of Azdia, have been destroyed or enslaved. The only hope for the creatures of Azdia are the awaited chosen ones sent from another world called Earth. The problem is Del Ryder has decided she never wants to go back.
She feels like it's all her fault that the Crystal Seeds are in the hands of the evil Heir of Mordlum. She's given up on her lumen friends thinking it is all too late. But when a bird shows up with a message, and Del's annoying older sister, Suzanne, is whisked away to Azdia in a way that no one saw coming, Del and her friends have no choice but to follow. Will they be able to mount a rescue before Suzanne is corrupted by the forces of darkness? And might they finally discover the key to restore the light and remake the world?