Rebecca is a six and a half year-old girl who is out of luck ― her parents are on the verge of divorce and she is always getting sick due to a weak immune system. One rainy day Rebecca's luck changes when she meets a magical microbe named Ernest, who becomes her best friend! Ernest is no regular germ; he's about the same height as Rebecca and he can talk. Can Rebecca keep her parents together with the help of her new friend? And can anyone really have a friend who belongs in a Petri dish?