Rituals. The Cainsville Series

The fifth book and the exciting conclusion to bestselling author Kelley Armstrong's "impossible-to-put-down" Cainsville series, in which she mixes hard-hitting crime writing with phenomenal world-building to create a brand of fiction all her own. When Olivia Taylor-Jones found out she was not actually the adopted child of a privileged Chicago family but of a notorious pair of convicted serial killers, her life exploded.
Running from the fall-out, she found a refuge in the secluded but oddly welcoming town of Cainsville, Illinois, but she couldn't resist trying to dig out the truth about her birth parents' crimes. She began working with Gabriel Walsh, a fiendishly successful criminal lawyer who also had links to the town; their investigation soon revealed Celtic mysteries at work in Cainsville, and also entangled Olivia in a tense love triangle with the calculating Gabriel and her charming biker boyfriend, Ricky.
Worse, troubling visions revealed to Olivia that the three of them were reenacting an ancient drama pitting the elders of Cainsville against the mysterious Huntsmen with Olivia as the prize.     In the series' fifth and final novel, not only does Gabriel's drug addict mother, who he thought was dead, make a surprise reappearance, but Kelley Armstrong delivers a final scary and surprising knock-out twist.
It turns out a third supernatural force has been at work all along, a dark and malevolent entity that has had its eye on Olivia since she was a baby and wants to win at any cost.