Returning from a business trip in Hong Kong, Beth Emhoff has a layover in Chicago to have sex with a former lover. Two days later, in her family home in suburban Minneapolis, she collapses with seizures. Her husband, Mitch Emhoff, rushes her to the hospital, but she dies of an unknown cause. Mitch returns home and finds that his stepson Clark has died from a similar disease. Mitch is put in isolation but is found to be immune; he is released and returns home to his teenage daughter Jory.