The group of amateur adventurers, led by a young woman named Terry, arrives in Shookum Hills to conduct an expedition into the mine that caused the town's downfall. They soon discover that the mine is much deeper than they anticipated, and also encounter strange occurrences such as unexplainable noises and an underground river that seems to flow uphill.
As they delve deeper into the mine, they uncover evidence of a sinister government experiment involving the use of human test subjects, and also encounter a group of mutated creatures that have adapted to the subterranean environment. The group is forced to fight for survival as they try to make their way out of the mine and back to the surface.
However, the local sheriff, who warns the group about the dangers of the mine and advises them not to enter, ultimately leads a rescue mission after they fail to return. The group must work together with the sheriff to escape the mine and stop the government experiment before it's too late. But, they soon realize that their biggest threat may not be the mutated creatures or the government experiment, but rather something much more sinister lurking in the shadows.