Blood Moon by Charlotte Raine
Aaron Grant is feeling hopeless, faithless, and singled out for tragedy. After losing his wife, his daughter, and now his foster son, Aaron tries to find himself again, which reluctantly includes getting help from his old pastor. At the same time, Sarah Latham finds herself joining a cult that believes the end of the world is coming, and their job is to purge all evil from existence. In apocalyptic mayhem, Sarah plays a major part in their plans of murder, while Aaron tries to track down his son's killer, while also figuring out his relationship with Teresa. As the perceived end-time begins to creep closer, the only guarantee is that Satan is more than a personification of evil—sometimes he exists inside people, pulling them into the darkness.