During the siege of Richmond, Virginia, in the American Civil War, POW Capt. Cyrus Harding escapes from his Confederate captors in a rather unusual way – by hijacking an observation balloon. In his escape, Harding is accompanied by sailor Pencroft, his nephew Bert, writer Gideon, loyal soldier Neb, and a dog. A hurricane blows the balloon off course, and the group eventually crash-lands on a cliff-bound, volcanic, uncharted (and fictitious) island, located in the South Pacific, with very unusual inhabitants. They name it "Lincoln Island" in honour of American President Abraham Lincoln. With the knowledge of the brilliant engineer, the five are able to sustain themselves on the island, producing fire, pottery, bricks, nitroglycerine, iron, a simple electric telegraph, and even a seaworthy ship. They also manage to find their geographical location.
The castaways soon encounter a group of people that include the local natives (who worship the island's volcano), Rulu (a woman from Mercury trying to extract an unnamed superexplosive element in order to conquer the Earth), Ayrton (a wild man exiled on the island) and Captain Shard (a ruthless pirate). A mystery man, who possesses great scientific powers, also makes his presence known to the group of people; he is Captain Nemo, who survived the whirlpool in 20,000 Leagues Under the Sea, and unlike the character in the Disney film, was not fatally wounded by military troops from warships. On the way, our quintet of heroes must battle the elements and peoples while trying to figure out a way off the island and back to civilization.