The Testament of Loki — Joanne M. Harris

In the sequel to The Gospel of Loki, Loki's adventures continue when he finds a way out of the end of the world and plans to restart the power of the Norse gods.

The end of the world -- also known as Ragnarok to the Norse gods -- has occurred, and Loki has been trapped in a seemingly endless purgatory, in torture, until he finds a way to escape. It seems that he still exists in the minds of humanity and uses that as a way to our time.

Back in the ninth world (Earth), Loki finds himself sharing the mind of a teenage girl named Jumps, who is a bit of a mess. She's also not happy about Loki sneaking his way into her mind, since she was originally calling on Thor. Worse, her friends have also been co-opted by the gods: Odin, Jump's one-eyed best friend in a wheelchair, and Freya, the pretty one. Thor escapes the netherworld as well and shares the mind of a dog, and he finds that it suits him.

Odin has a plan to bring back the Norse gods ascendancy, but Loki has his own ideas on how things can go -- and nothing goes according to plan.