Hercules, having agreed to restore justice to Mycenae, confronts evil Prince Myles. The villain is invested with power over giant bronze warriors by his mother Pasiphaë, a sorceress in Hades. Myles assassinates the king and abducts his cousin, Queen Ate, through whom he plans to inherit the throne. Although Zeus temporarily removes Hercules' strength for killing Eurystheus, an innocent man framed by Myles, the god restores his powers. Hercules then saves Ate and destroys Myles, Pasiphaë, and the giant warriors.

The eternal Hercules in this film has gone way beyond his usual time and place in ancient Greece and is now helping Poland free itself of Mongol invaders in the 12th century. Mark Forest is the star of this peplum epic, Hercules Against The Barbarians.

Though Genghis Khan eventually sought peace with the West, his death in 1227 AD puts into power his three war-like sons: Sayan, Susdal, and Kin Khan. These sons quickly overrun the city of Tuleda and take prisoner Princess Bianca, though young Prince Alessio escapes. Hercules comes to the rescue of Bianca, winning her freedom in a tournament in exchange for becoming a slave himself. Forces from the West soon come to re-take Tuleda and Hercules -- freed from his bonds -- helps to dispatch Genghis Khan's three sons while again saving Bianca and reuniting her with her young brother.

In order to persuade the Emperor to spare his village, the mighty Ursus is forced to fight the greatest gladiator in Rome in the Roman Arena.