The book 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 (named Cyrus Harding in some English translations); his black manservant Neb (short for Nebuchadnezzar), a former slave who had been freed by Smith; the sailor Bonadventure Pencroff (who is addressed only by his surname, but his "Christian name," Bonadventure, is given to their boat; in other translations, he is also known as Pencroft); his protege Harbert Brown (called Herbert in some translations), a young boy whom Pencroff raises as his own after the death of his father (Pencroff's former captain); and the journalist Gedeon Spilett (Gideon Spilett in English versions). The company is completed by Cyrus' dog "Top.""