Satan's Lambs — Lynn S. Hightower

A fearless female private investigator in the South takes on a satanic cult that practices human sacrifice in this gripping Shamus Awardâ€"winning mystery.
 
Seven years ago Lena Padget's life exploded when Jeff Hayes, her devil-worshipping brother-in-law, killed her sister and two-year-old nephew. The horrific double-murder hardened the once-gentle Kentucky native and compelled her to leave graduate school in order to help protect abused and endangered women from human monsters.
 
Now Hayes and his sadistic partner in satanism, Archie Valetta, have been inexplicably released on parole. Lena's past has returned with a vengeance to haunt her -- and to prey on yet another frightened mother and her helpless child. Approached by Valetta's desperate ex-wife, Eloise, Lena will do everything in her power to prevent history from repeating itself. Otherwise, Eloise's four-year-old son will be the next innocent victim.
 
Before Laura Lippman's Tess Monaghan and Karin Slaughter's Sara Linton, there was Lena Padget. The winner of the Shamus Award for Best First Private Eye Novel, Satan's Lambs marked the acclaimed debut of author Lynn Hightower's tough-as-nails, sexy, and smart female sleuth on a fictional PI scene long dominated by male mystery writers and established Hightower as a force to be reckoned with in crime fiction.
 
Satan's Lambs is the 1st book in the Lena Padget Mysteries, but you may enjoy reading the series in any order.