In the future, after global warming, Earth is covered by ice and snow in an Ice Age. The survivors live in facilities underground named Colonies. When people from Colony 5 release a distress signal, the leader of Colony 7 Briggs organizes an expedition with Sam and Graydon to investigate what has happened to their acquaintances. Briggs leaves the scientist Kai in charge of the group, disappointing his former friend Mason that expected to be assigned to the position. They walk for two days to reach the facility where fifty persons live and they find only one survivor that is scared to death locked in a room. Soon they learn that a savage group of cannibals have slaughtered the colonists. Briggs and Sam manage to escape but the group hunts them down. Briggs sacrifices his life to blow up a bridge and slow down the group while Sam heads to Colony 7. When Sam arrives, Mason has taken the power and cuffs him, and does not believe on his words. Soon the cannibals arrive and the group has to fight to survive.