When the world was invaded by underground creatures that wanted to wipe out mankind from Earth, the post-apocalyptic survivors called The Day of Reckoning. Fifteen years later, people have the same signs indicating that a new attack is coming and they seek out shelter for protection. What will happen to mankind this time?

Upon taking her vows to become a nun, Sister Sarah is abused, brainwashed and drugged into submission by the corrupt clergy. On the verge of death from a lethal dose of drugs, Sister Sarah receives a message from GOD telling her to take vengeance on all those who did her wrong. Armed with God's will and an arsenal of big guns, she dispenses Judgment Day on her former tormentors. When the church hires the merciless motorcycle gang the "Los Muertos" to track down and kill her they soon realize that this SISTER IS ONE BAD MOTHER.