A subterrainian race of monsters has been released due to human encrouchment. It's up to the Earth Corps team and the Mutors, Redwoods and Granites, to round them up and put them back where they were but the task won't be easy due largely in part to a corrupt Senator who gave in to the demands of a man named Blackthorne Shore. He bullies Senator Masterson into cutting Earth Corps's funding and giving their technology to him. If not for Blackthorne's sister Sandra and her desire to work with Earth Corps they would be doomed.