It's no one's fault that Hallie Jacob is alone. That her grandpa got sick half a world away and so her parents yanked her to Colorado the last semester of her senior year. That career-wise, she's specialized in fighting fire, and now she's surrounded by ice, snow, and a thousand cousins she's half-banned from hanging around with. But that's what's happened. That's what her December looks like.

On one big family weekend in the freaking tundra, Hallie sneaks off with those cousins to an abandoned ski slope. But they get caught in a random mudslide, and what started as a Secret Bonfire Party goes in a Potential Donner Party direction real fast. With some cousins in desperate need of medical attention, Hallie leaves their camp for help--and is surprised when Jonah Ramirez (her cousin's extremely off-limits--absurdly hot--best friend) joins her.

Facing paralyzing temperatures, sharp-toothed animals strong enough to survive a climate with hardly any water or air, and weather phenomena so wicked they'll wreck a mountain before you can blink, Jonah and Hallie have no choice but to trust each other as they search for the way to town to send help back to their stranded friends and family. And THAT may be more impossible, even, than making it out alive.