Fear the Darkness by Becky Masterman
Brigid Quinn has been shot at, stabbed in the spleen with a nail file and used as serial-killer bait. But she's always been able to trust her instincts and her FBI-training to help her out of danger.
Now, retired from the Bureau and investigating the tragic death of a neighbour's teenage son, Brigid starts to suffer unexplained bouts of paranoia, hallucination and memory loss. And for the first time in her life, she feels vulnerable.
But with a mass poisoning at the church, a dead man found in town and a grieving family convinced their son's death wasn't an accident, Brigid needs to put the pieces together - fast. Because evil has entered her life once more, and it's much closer than she thinks . . .