The witching tree : a Natalie Lockhart novel / Alice Blanchard.

Enhanced descriptions from Syndetics:

Welcome to Burning Lake, a small, isolated town with a dark history of witches and false accusations. Now, a modern-day witch has been murdered, and Detective Natalie Lockhart is reluctantly drawn deep into the case, in this atmospheric mystery from Alice Blanchard, The Witching Tree .

As legend has it, if you carve your deepest desire into the bark of a Witch Tree, then over time as the tree grows, it will swallow the carvings until only a witch can read them.

Until now.

Detective Natalie Lockhart gained unwanted notoriety when she and her family became front and center of not one, but two sensational murder cases. Now she's lost her way. Burned out and always looking over her shoulder, Natalie desperately thinks that quitting the police force is her only option left.

All that changes when a beloved resident--a practicing Wiccan and founder of the town's oldest coven--is killed in a fashion more twisted and shocking than Natalie has ever seen before, leaving the town reeling. Natalie has no choice but to help solve the case along with Detective Luke Pittman, her boss and the old childhood friend she cannot admit she loves, even to herself. There is a silent, malignant presence in Burning Lake that will not rest. And what happens next will shock the whole town, and Natalie, to the core.