Messalina was the Roman noblewoman who inveigled ageing emperor Claudio into marriage. Once ensconced on the throne, Messalina launched a reign of terror that shook the empire to its very foundations. The subject of countless film treatments, Rome's most villified empress is herein played by British actress Belinda Lee.

Upon his return from battle in the previous film, the great warrior Hercules learns that his lover, Daianara, has lost her senses. Acording of the oracle Medea, Dianara's only hope is the Stone of Forgetfulness which lies deep in the realm of Hades. Hercules, with two companions, Theseus and Telemachus, embarks on a dangerous quest for the stone, while he is unaware that Dianara's guardian, King Lico, is the one responsible for her condition and plots to have the girl for himself as his bride upon her revival.

In fascist Italy, Urbano Marangoni aspires to become Corazziere, like his late father, but it is a dream destined not to come true because of his short stature.

Alberto Menichetti lives with an aunt and an old housekeeper, Clotilde; he has a job in a firm and his boss is Mrs. De Ritis, a widow whose husband was killed during a wild boar hunt. She likes him but Alberto likes Marcella; she is under age and he is awaiting her birthday to declare his love. His greater traits are to be fearful of everything and to be selfish. This nature will get him into trouble..

King Androcles of Thebes commands a ship in search of a threat to Greece, predicted by an atmospheric oracle. Hercules is part of the crew, but the strongman falls overboard in a thick fog. Washed ashore, he saves a young Ismene from Proteus, an evil, shape-shifting creature. Ismene takes Hercules to Atlantis, where he discovers that her mother, Queen Antinea, has captured Androcles. Hercules schemes to rescue him and thwart Antinea's dream of world conquest.

Angélique is in a North African Muslim kingdom where she is now part of the Sultan's harem. She refuses to be bedded as her captors try to beat sense into her. She finally decides to escape with the help of two Christian prisoners.

While he is trying to escape from a hit man, Carl is setting up a kidnapping in Beirut. He gets lost on his way, falling in love with Salène, a.k.a. "La grande sauterelle"...

For the past few weeks, revolt has been brewing in the Kingdom of Naples. The handsome Castelli is at the head of the conspiracy that wants to put an end to the reign of King Murat. To carry out his plan, he decides to infiltrate the court in order to become an intimate of the king. But his ploy works too well: he manages to enter the court thanks to his talents as a singer and very quickly seduces Queen Geneviève. But this imprudence costs him a lot. He is soon arrested by the king's men and immediately condemned to death.

Carlo, a young doctor, occasionally meets Anna, the daughter of professor Valli. Carlo falls in love with Anna, who returns his feelings; but her father longs a brilliant marriage for her.