Underground, in the labyrinth of ancient tunnels and mine shafts, Lilly Caul and her motley crew of senior citizens, misfits, and children struggle to build a new life. Way out in the hinterlands, the psychotic Reverend Jeremiah Garlitz rebuilds his army of followers with a diabolical secret weapon. He has designs on the destruction of Lilly and her crew and now, for the first time, he has the means to bring a special brand of hell down upon the tunnel dwellers. The final confrontation between these two human factions unleashes an unthinkable weapon – forged from the monstrous hordes of undead, perfected by a madman, and soaked in the blood of innocents.