The Mysterious Island is Jules Verne’s unofficial 1874 sequel to both Twenty Thousand Leagues Under the Sea and In Search of the Castaways.

The story tells the adventures of five Americans on an uncharted island in the South Pacific. The story begins in the American Civil War, during the siege of Richmond, Virginia, the capital of the Confederate States of America. As famine and death ravage the city, five northern prisoners of war decide to escape by the unusual means of hijacking a balloon.

The escapees are Cyrus Smith, a railroad engineer in the Union army; his manservant Ne; the sailor Bonadventure Pencroff; his protégé Harbert Brown, a young boy whom Pencroff raises as his own after the death of his father; and the journalist Gedéon Spilett. The company is completed by Cyrus' dog Top.

After flying in stormy weather for several days, the group crash-lands on a cliff-bound, volcanic, unknown island, described as being located somewhere east of New Zealand. The island has a secret: it is Captain Nemo's hideout and home port of The Nautilus...