Now that Detective Charlie Madigan knows the off-world drug ash makes humans the perfect vessels for possession, she'll do anything to save her addicted sister Bryn. But as New Year's Eve approaches and ash victims began taking their own lives, Charlie is out of time. And worse, every exorcist in Atlanta has fled, leaving no one able to "see" who among the addicted are possessed and in danger. Desperate for help, Charlie turns to an ancient race of beings-creatures of mist and smoke, and embarks on a journey into hellish Charbydon with her siren partner Hank and the Revenant Rex to save Bryn and make it back before the creatures exact their deadly price. But one of them isn't coming home....