Midnight is the Darkest Hour by Ashley Winstead

From the critically acclaimed author of In My Dreams I Hold A Knife and The Last Housewife comes Midnight is the Darkest Hour, a gothic Southern thriller about a killer haunting a small Louisiana town, where two outcasts—the preacher's daughter and the boy from the wrong side of the tracks—hold the key to uncovering the truth.
For fans of Verity and A Flicker in the Dark, Midnight is the Darkest Hour is a twisted tale of murder, obsessive love, and the beastly urges that lie dormant within us all...even the God-fearing folk of Bottom Springs, Louisiana. In her small hometown, librarian Ruth Cornier has always felt like an outsider, even as her beloved father rains fire-and-brimstone warnings from the pulpit at Holy Fire Baptist. Unfortunately for Ruth, the only things the townspeople fear more than the God and the Devil are the myths that haunt the area, like the story of the Low Man, a vampiric figure said to steal into sinners' bedrooms and kill them on moonless nights. When a skull is found deep in the swamp next to mysterious carved symbols, Bottom Springs is thrown into uproar—and Ruth realizes only she and Everett, an old friend with a dark past, have the power to comb the town's secret underbelly in search of true evil.
A dark and powerful novel like fans have come to expect from Ashley Winstead, Midnight is the Darkest Hour is an examination of the ways we've come to expect love, religion, and stories to save us, the lengths we have to go to in order to take back power, and the monstrous work of being a girl in this world.
"Where The Crawdads Sing meets Twilight meets Thelma and Louise in this brilliantly realized, totally original thriller. Absolutely sensational—I couldn't put it down." —Clare Mackintosh, New York Times bestselling author