Cali Evans is a survivor. Her life hasn't been easy, but her late father raised her to be smart, tough, and dependent only on herself and her wits. On the eve of her 21st birthday she meets Owen Bray - a beautiful and intriguing young doctor who equally frustrates and captivates Cali. That fateful meeting inspires Cali to make a better life for herself.

The next day, hoping to make positive change, Cali hops a bus for the West Coast but never reaches her destination. Instead, she wakes up in an underground bunker with no recollection of how she got there. Upon her arrival, she learns that she's one of just forty survivors of a fast-spreading environmental toxin and that human life outside of the bunker has ceased to exist.

Tired of the vague explanations and half-answers coming from the people in charge, Cali takes it upon herself to investigate the real reason why she's there and begins to uncover the sinister truth.