Hannah awakens to carnage, all mangled metal and shattered glass. During a hasty escape from a secluded boarding school, her schoolbus careened over a hillside road during one of the year's heaviest snowstorms, trapping her inside with a handful of survivors, a brewing virus and no way to call for help. If she and the remaining few want to make it out alive, with their sanity--and secrets--intact, they'll need to work together or they'll be buried alive with the rest of the dead. A former detective, Meg awakens to a gentle rocking. She is in a cable car suspended far above a snowstorm and surrounded by strangers in the same uniform as her, with no memory of how they got there. They are heading to a mysterious place known only to them as "The Retreat," but when they discover a dead man among their ranks and Meg spies a familiar face, she realizes that there is something far more insidious going on and begins to use the skills from her former life to interrogate her fellow passengers. Carter is gazing out the window of the abandoned ski chalet that he and his ragtag compatriots call home. As the years drag on, the view of pine forests and mountaintops has become wallpaper. Together, they manage what they can to survive--mostly manufacturing vaccines against a deadly virus in exchange for life's essentials. But as their generator begins to waver, the threat of something lurking in the chalet's depths looms larger, and their fragile bonds will be tested when the power finally fails--for good. The imminent dangers faced by Hannah, Meg and Carter are each one part of the puzzle. Lurking in their shadows is an even greater threat--one that threatens to consume all of humanity.