Killing rites - M. L. N Hanover

Jayn 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 Jayn before the parasite in her becomes too powerful.

Ex's history and a new enemy combine to leave Jayn 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. Jayn 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.