Life isn't easy for Rebecca. Between parents at each other's throats, a big sister with her own worries, and an uncle intent on her taking her medicine, it's hard for Rebecca to keep smiling. Complicating things further, her health isn't good and her parents would prefer she be cloistered all the time. But Rebecca has a solution to her problems: Ernest the bacterium who's become her sworn pal and is out to reconcile her parents and fight off a new virus named Sam who threatens to make Rebecca's health take a turn for the worst!