Over the course of the first season, the group increasingly encounters threats originating from Valhalla Sector, which they discover to be a sealed and heavily armed bunker complex in West Virginia, used to house the remains of the US government and military leadership during the Big Death. The survivors there plan to rebuild the world in an authoritarian mold, combining their military power with attempts to control the "Big Death" virus itself in order to wipe out resistance by slaughtering non-compliant populations. The second half of Season 1 primarily deals with the efforts of Jeremiah and Thunder Mountain to stop Valhalla Sector.