Plot:
King Androcleas of Thebes goes to see the prophets for the starnge things that have been happening lately. All he learns is some "danger from afar" warning. He tries to unite the other Kings of Greece. However, none of them will unite against the threat.
Hercules's wife, Ayonsara, doesn't want him or their son, Hyus, to go with Androcleas. Hercules refused the king and vowed to watch the kingdom instead. He goes to see his friend off. Hyus is hiding belowdecks (he always wanted to go off but didn't want dear old dad to know.) Androcleas and Timocleus, the midget, spike Hercules's drink. Several hours later, Hercules awakens and finds they took him on the boat with them.
A storm hits the ship, and Androcleas is thrown overboard. Before, Hercules can do anything, the ship gets torn
apart. Hercules reaches an island and finds Ismene chained to a cliff. Proteus (or what looks like a deformed Gorn from Star Trek) attacks Hercules.

Captain Kirk will fight the Gorn a couple of thousands from now..
Proteus apparently can morph into various creatures like Animal Man. Proteus in a lion suit jumps the hero. Of course, Hercules defeats him.
Hercules and Ismene are teleported to Atlantis. He walks into the temple.

This is a lair for an evil queen.
Antonea, Queen of Atlantis, isn't happy with Atlanis's cloaking field quitting or the fact that her daughter, Ismene,
is among those of the living. The queen thanks Hercules.
The Queen knew all along that her daughter would have to be sacrificed so Atlantis would survive.
Hercules thinks he sees Androcleas.
Hyus and Timocleus reach the beach of Atlantis. They see soldiers tie Ismene to a pole.

We'll tie you to the stake and not let any Ray Harryhausen monsters get you.
Well, these two decide they better do something about it and rescue the girl.
Hercules is enjoying the palace entertainment but refuses to stay and will start searching for Androcleas. That night, a guard attacks Hercules. He's shocked to discover that it's Androcleas rambling on the strength of Atlantis and the destruction of Greece. The Queen walks up and apologizes for the guard's insanity.
Queen learns that her daughter was rescued by some strangers. The bringer of the bad news gets dropped into a pit
of acid.

All evil overlords need some torturing dungeon.
That's not the Queen's only brilliant idea. She has been trying to create a new super race and those that don't cut the mustard are tossed in a pit.

No Stephen King's super flu remains in this area.
Timocleus, Hyus, and Ismene hide from the soldiers. They follow the soldiers after they realize Androcleus is with them and see the king dropped into a pit. Hercules catches up and discovers his friends on the island. He starts freeing the prisoners.
Apparently, a rock on Mt Death is what is being used for the Queen's eugenic program. Hercules heads off to destroy the rock and discovers the rock has the blood of Uranus. Queen wants to rule over humans and the Greek gods. Hercules is revealed the secret that sunlight may destroy the rock.
Hyus and Ismene of course fall in love. The freed Atlanteans decide now is the time to attack the city like any good angry mob would do.
The slaves mob the soldiers. Hercules discovers that the Queen has Hyus and offers to let Hercules to join her side. She siccs her super soldiers (who are as strong as Hercules) on Hercules when he refuses. He is imprisoned side by side with Hyus. They're able to lift the door to escape.
Hercules sends Hyus to get a boat ready for them while he finishes the rock. Hercules does the horse chariot version of the Molotov cocktail to set the super soldiers on fire. Reaching the mountain, he tears a hole in the roof of the cave so the sunlight may reach the rock.
Hyus finds Timocleus who tells him that the soldiers grabbed Ismene and Androcleus on the ship. Hyus reaches the ship and keeps it from being set afire.
Hercules jumps from the mountain and swims to the ship. The sunlight finally touches the rock which starts the stock volcanic footage. The palace collapses with the columns crushing the Queen to death. The island sinks into the ocean.
On the ship, Androcleas regians his memory but for the crazed Atlantean soldier, etc...