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 black manservant Neb (short for Nebuchadnezzar), a former slave who had been freed by Smith; the sailor Bonadventure Pencroft; his protégé Harbert Brown, a young boy whom Pencroff raises as his own after the death of his father (Pencroff's former captain); and the journalist Gedéon Spilett. The company is completed by Cyrus' dog "Top".
Mind you, they had escaped from Richmond and flown to the Pacific. On that.
Captain Nemo showed up, by the way, because Verne wasn't stupid.