When Gyre Price lied her way into this expedition, she thought she'd be mapping mineral deposits and the greatest dangers might be cave collapses and gear malfunctions. She also thought the fat paycheck meant she'd get a skilled surface team monitoring her suit and environment, keeping her safe. Keeping her sane. Instead, she got Em. Em sees nothing wrong with controlling Gyre's body with drugs or withholding critical information to "ensure the smooth operation" of her expedition. Em knows all about Gyre's falsified credentials, and has no qualms using them as a leash--and a lash. And Em has secrets, too . . . As Gyre descends, mounting inconsistencies--missing supplies, unexpected changes in the route, and, worst of all, shifts in Em's motivations--weigh on her more than the rocks overhead. Lost and disoriented, Gyre finds her sense of control giving way to paranoia and anger. On her own in this mysterious, deadly place, surrounded by darkness and the unknown, Gyre must overcome more than just the dangerous terrain and the Tunneler that calls the underground its home if she wants to make it out alive--she must confront the ghosts in her own head. But why can't she shake the feeling she's being followed?