From the liner notes

As Alcemene (Perkins), princess of Thebes, awaits the return of her husband Amphitryon (Dalton) from war, the virtuous bride falls victim to the licentiuous Zeus and finds herself carrying the great god's child. Born Hercules (Telfer), the strapping lad is rejected by his mother, envied by his brother Iphicles, and loatherd by Zeus's wife Hera.

Unbeknownst to Hercules, his wife and preistess Megara and her sons are merely tools of the vengeful Hera, plotting against him and initiating events that lead to banishment from his people.