Becca is a typical high school girl, except she's in love with her best friend, Natasha. But as she struggles with whether to tell Natasha her true feelings for her, the U.S. is attacked. The weapons used spread a fog which kills most, and leaves infected survivors as zombie-like monsters who crave blood. The attack spreads quickly, threatening the entire country, in a matter of hours.
To keep them safe, Becca’s father charges her with getting her little sister, Bridget, Bridget’s friends, and Tasha to the Colorado mountains while he and Becca’s mother go to help other family members to safety. Becca doesn’t want to be in charge, but is forced to take the lead.