Professor Andre and his companions are exploring the vast caverns of Greece, trying to unearth a priceless bounty of ancient artifacts. Their archeological dig turns deadly when an invisible creature with a bloodcurdling shriek is awakened, lashing out with a horrifying vengeance! When two people are brutally killed and another one critically wounded by the uncontrollable beast, Andre and his cohorts are forced to abandon their quest for riches and desperately fight for their lives.<P>Originally released as <i>El Sonido Prehistorico</i>, the film features Soledad Miranda and Ingrid Pitt, who would later enjoy cult stardom through a series of European horror films.