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 sister 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, giant squid and an eerie undiscovered humanoid race.

• Metro-Goldwyn-Mayer
• Lionel Barrymore
• Jacqueline Gadsden
• Lloyd Hughes
• Montagu Love
• Montagu Love
• Snitz Edwards
• Gibson Gowland
• Dolores Brinkman