An Exchange of Hostages (Chained Worlds Chronicles #4)

Description

His old friends are dead and now Derek is trapped as a human and branded by magic. Still, time moves on and he has made do. He's made new friends, a home, and learned various secrets of the universe. Then apocalypse came and went and after a well-deserved slumber, he was stuck dealing with an alien invasion.
After that inconvenience was worked out, he continues to work on his "To Do" list. This includes things like:
1) Master his various magics,
2) Mapping how and where the planets chained together,
3) Finding the Demon Lord's base dimension,
4) And of course, finding where his Norse elf wandered off to with several hundred elementals.
There is also figuring out what happened to Mars after the goddess Lamia single-handedly destroyed it. So much to do, so little time. Fortunately, he has a place to lay his head to rest in between errands... wait, didn't the aliens destroy that?