 On a volcanic island near the kingdom of Hetvia rules Count Dakkar, a benevolent leader and scientist who has eliminated class distinction among the island's inhabitants.Dakkar, his daughter Sonia and her fiance, engineer Nicolai Roget have designed a submarine which Roget pilots on its initial voyage just before the island is overrun by Baron Falon, despotic ruler of Hetvia.Falon sets out after Roget in a second submarine and the two craft, diving to the ocean's floor, discover a strange land populated by dragons, a giant octopus and an eerie undiscovered humanoid race.