At the end of the world, who do you save? With their numbers diminishing and the alien armies growing stronger, Sophie's biosphere decides to join forces with the team from NTC's submarine. Using data from a surviving satellite, they discover strange, alien poles at each of the world's seven highest summits: alien technology that the survivors believe may hold the key to shutting down the alien ships once and for all. That's not all. The satellite also discovers an encrypted set of coordinates that reveal SOS messages from US Military bases around the world, all activated on invasion day, except for one: Offutt Air Force Base. But before they can launch an offensive, the biosphere team must deal with sabotage from within and a strange nanotechnology that has infected several of the survivors. As tensions rise, Sophie and team must decide whether a new discovery at Offutt is worth abandoning the biosphere. The more the team learns, the more they realize the planet may be beyond saving and that salvation may require leaving the planet forever.