King Androcles of Thebes (Ettore Manni) commands a ship searching for a threat to Greece predicted by oracles. Hercules (Reg Park) is part of the crew, but the strongman falls overboard in a thick fog. Washed ashore, he saves a young girl, Ismene (Laura Altan), from a shape-shifting creature. She takes Hercules to Atlantis, where he discovers that her mother, the evil Queen Antinea (Fay Spain), has captured Androcles. Hercules schemes to rescue him and thwart Antinea's dream of world conquest.