Mark and his brother John are exterminators for Sector 7, a government organization that eliminates dangerous indigenous organisms on Salvadon, a relatively new colony in the far future. They uncover a strange parasite on a mission, capable of mutating hosts into beings with superior intelligence or outright killing them in minutes. On the same mission, Mark rescues Karen, an alluring yet mysterious woman who is hiding a terrible secret from the brothers; a secret that can endanger all of their lives.