From the description:
"When Billy's father mysteriously disappears and his mother responds by becoming more and more reclusive, Billy maintains hope that his father's absence is not by choice—despite the rumors and taunts of his classmates who believe otherwise. Twelve days before Christmas, Billy acquires a magical tree with a dozen ornaments, each of which holds a clue to finding his father. In order to do so, however, Billy must solve one puzzle each day, so he enlists the help of his best friend Katherine, not realizing that in doing so, he has placed them both in grave danger. The forces of evil that have captured Billy's father are revealed to be manifest in the landscape of their very own small hometown outside of Oxford, England, as well as in some of its seemingly benign inhabitants."
5 stars, but only on 5 reviews, so a bit of an unknown here. 313 pages. It appears to be for teens, so lets say age 12 and up.