Killing Rites (Black Sun's Daughter‪)‬

Jayné Heller has discovered the source of her uncanny powers: something else is living inside her body. She's possessed. Of all her companions, she can only bring herself to confide in Ex, the former priest. They seek help from his old
teacher and the circle of friends he left behind, hoping to cleanse Jayné before the parasite in her becomes too powerful.

Ex’s history and a new enemy combine to leave Jayné alone and on the run. Her friends, thinking that the rider with her has taken the reins, try to hunt her down, unaware of the danger they’re putting her in. Jayné must defeat the weight
of the past and the murderous intent of another rider, and her only allies are a rogue vampire she once helped free and the nameless thing hiding inside her skin.