At the unused Yucca Mountain nuclear waste repository in Nevada, a group of survivors briefly venture out of their underground refuge only to face a battle with hostile foreign survivors seeking to take their refuge. An attack from within causes much death and ignites military action.
They find themselves under surveillance by Islamic activists who survived in Central America and are moving into Nevada to take control of the Hoover Dam, which gives the Brotherhood control of the Colorado River and the electricity it generates for the western United States.
Both the activists and the survivors in the mountain realize the jet stream is returning the fallout of the nuclear winter back to the region. Both seek to replenish food and supplies needed to carry them through another siege by the nuclear fallout. The survivors in the mountain repel attacks on the mountain and enter the next phase of nuclear winter prepared to battle the Islamic State and drive them from the region.