The Immortals By J.T. Ellison

It is Samhain–the Blood Harvest. Nonbelievers call it Hallowe’en. The night when eight Nashville teenagers are found dead, with occult symbols carved into their naked bodies. It’s a ritual the killers believe was blessed by Death himself.
When children are victimized, emotions always run high, and this case has the public both outraged and terrified: a dangerous combination. Recently reinstated homicide lieutenant Taylor Jackson knows she has to act quickly, but tread carefully.

Exploring the baffling culture of mysticism and witchcraft, Taylor is immersed in a darkness that threatens to unbalance the order of her world, and learns how unchecked wrath can push a killer to his limits.