Three thousand two hundred years ago, the tyrannical King Cotys is determined to unite the quarrelsome tribes of Thrace into a single, belligerent nation. Cotys has hired Hercules and his fellow mercenaries to mould his troops into an invincible army of destruction. Now the training is over, and Hercules leads that army in a bloody war of attrition against Rhesus, Cotys's last significant foe. However, just as victory seems secure, it appears that treachery is afoot, and the potential consequences are dire, particularly for Hercules and his friends!