To save her sister, she must stop a silent killer. . . . Protecting Atlanta from the off-world criminals of Underground is tough enough, but now Detective Charlie Madigan and her siren partner, Hank, learn that the addicts of the offworld drug ash have begun taking their own lives. Ash makes humans the perfect vessels for possession, and something or someone is leading them to their deaths. Charlie is desperate to save her addicted sister, Bryn, from a similar fate. As New Year's Eve approaches and time runs out, Charlie makes a deadly bargain with an ancient race of beings and embarks on a dangerous journey into hellish Charbydon with Hank and the Revenant Rex to save Bryn and make it back before it's too late. Only, for one of them, coming home means facing a fate worse then death. . . .