The Rise of Sturd. The Coal Elf Chronicles, #2

You can't keep a bad elf down. Upon completing her first Big Night assignment-delivering coal to all the kids on the naughty list-Ember Skye thought all was well at the North Pole. She no longer has to slave away in the coal mines, and her arch-nemesis has seemingly been stripped of his power. Sturd, however, has only been biding his time. After he discovers an ancient text, the demonic elf sets out on a mission that could change life at the Pole as they know it.
His rise in power could threaten the very existence of the Big Night, the North Pole, and even Claus himself. Return to the North Pole where Ember and all the coal elves will soon realize never to underestimate the corruptible temptation of unrivaled power. Unfortunately for them, it may be too late. chaos may reign supreme.