The Four Corners of Darkness - C S Elston - Bog

Three years have passed since the Snyder family was taken to the strange world of Kadosh and separated onto islands to keep them apart from one another. Their return home saw each of them forever changed by the journey they embarked on to reunite. Now a cohesive unit, the Snyders have also been changed by their quest to learn more about the source of the light they encountered on Raum's island.
While it was Raum who had initially snatched them out of their world and into his, they now find themselves being called to go back but, this time, the calling is coming from the source of that very same light. And, an old friend is being called to go with them.
The group agrees to return and use their experience to show others who are still being held captive the way out. But, when they get there, they find that all of Kadosh has been trapped in darkness. Dawn hasn't been seen since the Snyders left, and it is clear that their second journey out of Kadosh will be even more difficult than the last one.