Aliens from the constellation Hydra crash-land on the island of Sardinia. A prominent scientist, his daughter, several young technicians, and a pair of Oriental spies are taken hostage by the beings so they can use them to repair their spaceship's broken engine. With that done, they take off towards their home planet, taking the earthlings with them. However, the humans attempt to mutiny against their captors, inadvertently sending their tiny spaceship hurtling into the infinite beyond...

In this melange of characters and events from separate mythological stories, Hercules, demigod and superman, arrives in the ancient Greek kingdom of Iolcus to tutor Iphitus, son of king Pelias; immediately on arrival, he falls in love with the king's delectable, briefly clad daughter Iole. Before he can win her, he must succeed in a series of quests, in the course of which he teams up with Jason, true heir of Iolcus, whom he accompanies on the famous voyage of the Argonauts.

En route to Thebes for an important diplomatic mission, Hercules drinks from a magic spring and loses his memory. He spends most of the movie in the pleasure gardens of Queen Omphale of Lydia. While young Ulysses tries to help him regain his memory, political tensions escalate in Thebes, and Hercules' new wife Iole finds herself in mortal danger.