With Rudolph facing off against Santa, Christmas is on the line, along with her freedom.

Ru was born in a forest and soon recruited by Santa. He wanted her to help harness the remains of long-dead deities. Christmas is coming into fashion in the human world and that is a lot of energy to take advantage of. He moves her back in time, and together, they build the workshop.
Ru has one problem. Santa tricked her and locked the collar around her neck. Her other forms are no longer hers to command, and without them, she can't be whole.
It has taken her over a thousand years, but she finally has a way to claim her freedom, and if Santa cooperates, Christmas won't be hurt.