With the exception of losing her older sister in a hit-and-run, 17-year-old Tia Scott has had a pretty normal life. That is until she starts exhibiting strange symptoms and realizes she's caught a virus that's slowly turning her into a zombie. Desperate to find a cure, the only person she trusts is a loner at school, Flynn, a self-proclaimed expert in all things paranormal. But Tia's life gets even worse when a friend of her boyfriend, Connor, is murdered. Tia knows that Connor's friend Jason is involved but going to the cops makes her a target and with the clock ticking until Tia's too far gone to recover, she enlists the help of her mother Kate and a reclusive doctor in hopes they'll stop the disease before Jason finds out she's the snitch.

In an effort to get away from their problems for a little while during a particularly stressful holiday season, identical twins, Sophia, a single girl in the city with a demanding boss, and Kaelynn, a single mother of two in the Midwest, decide to switch places for Christmas.