Mentally disabled Karl Childers (Billy Bob Thornton) is released from the mental hospital where he has spent most of his life after murdering his mother and her lover. He soon forms a bond with Frank (Lucas Black), a boy whose father committed suicide. When Frank’s mother, Linda (Natalie Canerday), lets Karl stay at their house, her cruel boyfriend, Doyle (Dwight Yoakam), tries to get Karl removed. Determined to protect his friend, Karl devises a way to save Frank from years of Doyle’s abuse.
Repairmen Val McKee (Kevin Bacon) and Earl Bassett (Fred Ward) are tired of their dull lives in the small desert town of Perfection, Nev. But just as the two try to skip town, they happen upon a series of mysterious deaths and a concerned seismologist (Finn Carter) studying unnatural readings below the ground. With the help of an eccentric couple (Reba McEntire, Michael Gross), the group fights for survival against giant, worm-like monsters hungry for human flesh.