In the peaceful kingdom of Hetvia, Count Dakkar prepares two high-tech submarines to explore the ocean depths. Jealous of Hetvia's bounty and eager for war, the wicked Baron Hubert Falon attempts to steal the two submersibles for nefarious use. An undersea chase ensues, which leads the two rivals, along with Dakkar's daughter and her lover, into a secret world ruled by a race of strange aquatic creatures.