Hercules (Reg Park) and King Androcles (Ettore Manni) are on an ocean expedition when Androcles is washed overboard during a storm near a mysterious island. Making landfall, Hercules finds that the island is the kingdom of Atlantis, ruled by a beautiful, cruel, and ambitious queen, Antinea (Fay Spain), who controls a mysterious source of power. She has transformed her personal guard into super-strong warriors -- each nearly a match for Hercules, put Androcles under her spell, and inflicted terrible wounds on her people, all in preparation for her plan to conquer the world. Hercules finds that her power stems from a source older than the gods on Olympus, one over which he has virtually no power. He must save his friend, release Antinea's people, and prevent her from carrying out her plans.