During the US Civil War, Union POWs escape in a balloon and end up stranded on a South Pacific island, inhabited by giant plants and animals. They must use their ingenuity to survive the dangers, and to devise a way to return home. Sequel to '20,000 Leagues Under the Sea' .

Tianhuo Island is as beautiful as a paradise. It almost makes people forget that it is located in the "Ring of Fire" the world-famous Pacific Rim volcanic belt. The volcano erupts, and the fates of the people on the island are entangled.

As the world progresses into the industrial age, a professor studying the "nature of pure matter" is spirited away by a would-be dictator and connived into building a super-bomb, as a young reporter and a girl rescued from the sea attempt to warn him of their mutual kidnapper's intentions to dominate the world with a new and more-deadly-yet weapon.

During World War II, an American bomber pilot is rescued after drifting at sea aboard a raft. After being administered truth serum, he tells the doctor a story of how he and the three survivors of his plane crash washed up on an island that was inhabited by a tribe of beautiful primitive cave-women, dinosaurs and a group of savage cavemen who are bent on abducting the women for breeding purposes.

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.

With the help of diver and biologist Laurent Ballesta, a scientific expedition explores three sunken Italian volcanic sites in the Mediterranean.