Six years ago, a deadly virus contained in raindrops wiped out almost the entire population from the face of the Earth. An employee of the Appolo corporation, knowing of the impending catastrophe, managed to hide his children in a special bunker, ordered his daughter to protect her younger brother, and went off to save humanity. Six years later, the teens are running out of food, so the sister decides to surface to scout and soon heads out to search for their father, who never returned.