The Mysterious Island is a classic adventure novel by Jules Verne, first published in 1874. It follows a group of five men and a dog who escape from captivity during the American Civil War by hijacking a hot-air balloon. They are carried by the wind and eventually crash-land on a remote, uncharted island in the Pacific Ocean. The novel is notable for its themes of survival, ingenuity, and mystery, as well as for being a loose sequel to Twenty Thousand Leagues Under the Sea.

The story begins with five Union prisoners-engineer Cyrus Smith, journalist Gideon Spilett, sailor Pencroff, his adopted son Harbert, and former slave Nab-escaping from a Confederate prison in Richmond, Virginia. They are swept far off course by a storm while in the hot-air balloon and land on an unknown island, which they later name Lincoln Island.

The group, led by the resourceful Cyrus Smith, sets out to explore the island and ensure their survival. Using Smith's knowledge of science and engineering, they manage to build a new life on the island, constructing shelters, manufacturing tools, and even developing a basic form of agriculture. They display remarkable ingenuity in taming their environment and overcoming various challenges.

As they settle into their new life, strange and unexplained events begin to occur. For instance, Cyrus is rescued from a near-drowning under mysterious circumstances, and the castaways find items, such as a message in a bottle and advanced tools, which seem to have come from an unknown benefactor.

The group faces danger when a pirate ship arrives on the island. However, just when defeat seems certain, the pirate ship is destroyed in an unexplained explosion. Eventually, they discover that these interventions are the work of Captain Nemo, the enigmatic character from Twenty Thousand Leagues Under the Sea. Nemo, who has been living secretly in his submarine Nautilus beneath the island, has been assisting the colonists from afar.

The colonists meet the dying Captain Nemo, who reveals his identity and shares his history. He explains that he has been watching over them and subtly helping them throughout their time on the island. After Nemo's death, the island is revealed to be volcanic, and it eventually erupts, destroying most of the island.

As the volcano threatens to obliterate everything, a passing ship, alerted by the castaways' earlier signals, rescues them. They return to civilization, having survived countless challenges through cooperation, intellect, and perseverance.