The Redeemed — Jonas Saul

Four Catholic priests have been murdered in Los Angeles, each killed in a different way. Each priest's name is carved into a small crucifix found with the body. Someone with a deep-rooted hatred of Catholicism is targeting priests with a suspected history of deviant behavior.
The lead detective, David Hirst, calls on his friend Parkman for help and asks if he could bring Sarah Roberts along. Since Sarah is on a quest to redeem herself with her colleague Parkman after she had let him down in the past, she agrees to go to L.A. and do whatever she can to aid in the investigation.
When they arrive, they head straight to the crime scene of yet another dead priest. With Sarah's history of antagonizing cops, and a recent feature in newspapers around North America regarding the death of a Canadian officer, the LAPD don't want her help. Within days, Hirst regrets his decision and asks Sarah and Parkman to leave.
But the killer has other plans. According to the Bible, since Sarah is an automatic writer and talks to her dead sister, she is a practitioner of witchcraft and she works for the devil. Therefore she has to die, too.
Before she has a chance to leave L.A., the priest killer has carved her name into a small crucifix.
What he has in store for her is reminiscent of Eve in the Garden of Eden, a snake and a very painful way to die.
Sarah has the will to live, the tenacity to fight, and a little help from her sister on the other side as Vivian digs deep to change the way she sends messages to Sarah.
But channeling through Sarah's body and whispering to her takes a toll on Sarah, and she begins to feel and see Vivian's thoughts and memories. While Sarah fights to save herself, she's also trying to save her sanity as two vie for her consciousness.