Plot
In 1868, rumors spread of a sea monster attacking many ships in the Pacific Ocean. Professor Pierre Aronnax and his assistant, Conseil, are asked to investigate the scene. They board a U.S. Navy frigate with Ned Land, a master harpooner.
After months of patrolling, the monster is spotted. The frigate's crew opens fire, but the monster rams the ship. Ned, Conseil, and Aronnax are thrown overboard, while the disabled frigate drifts away. While clinging to wreckage, Aronnax and Conseil come upon a metal vessel, realizing that the monster is a man-made "submerging boat", which appears deserted. Below deck, Aronnax finds a large viewport and witnesses an underwater funeral, while Ned arrives on an overturned longboat from their ship.
Spotted by the divers, Ned, Aronnax, and Conseil attempt to leave in the longboat, but they are captured. The vessel's captain introduces himself as Captain Nemo, master of the Nautilus. He returns Ned and Conseil to the deck while offering Aronnax the chance to stay. After Aronnax proves willing to die with his companions as the ship submerges, Nemo allows Ned and Conseil to remain aboard. He explains that he has intentionally withdrawn from civilization, and that the sea provides all he needs. Arronax is amazed by Nemo's discoveries and inventions, including the advanced technology of the Nautilus and the crew's ability to harvest an abundance of sea creatures for food.
The Nautilus arrives at a penal colony island, where the prisoners are loading a munitions ship. Nemo, who was once a prisoner there, rams the ship and destroys it. Nemo tells Aronnax that he has just saved thousands from death in war, and that "this hated nation" tortured his wife and son to death while attempting to force him to reveal his discoveries. In Nemo's cabin, Ned and Conseil discover the coordinates of Nemo's secret island base called Vulcania, where the Nautilus is now heading. Hoping to be rescued, Ned loads bottles with the coordinates and throws them overboard.
Off the coast of New Guinea, the Nautilus becomes stranded on a reef. Nemo allows Ned to go ashore with Conseil, ostensibly to collect specimens, while admonishing them to stay on the beach. Ned instead goes exploring for avenues of escape, and finds human skulls posted on stakes. Ned runs back to Conseil, and they row away pursued by the cannibals. Aboard the Nautilus, the cannibals are repelled by electrical charges sent through its hull, and Nemo confines Ned for disobeying orders.
A warship fires upon the Nautilus, which descends into the depths, attracting a giant squid. After an electric charge fails to repel the creature, Nemo and his men surface to fight it off. Nemo is caught by one of its tentacles, and Ned, having escaped from captivity, fatally harpoons it. He then saves Nemo, who had been pulled into the sea. Having had a change of heart, Nemo decides to make amends with human civilization.
The Nautilus enters Vulcania through an underwater passage to avoid the warships that now surround it. Nemo rushes ashore to activate a time bomb, which will destroy all evidence of his discoveries, but he is shot and mortally wounded as he returns onboard. Nemo announces that he will be sinking with the ship, and the crew agrees to accompany him.
Aronnax, Conseil, and Ned are confined to their cabins. Refusing to be part of the suicide pact, Ned escapes and brings the submarine to the surface. The Nautilus strikes a reef and begins to flood. Nemo dies while viewing his beloved undersea domain through the hull's viewport.
Aronnax tries to retrieve his journal, but the urgency of their escape obliges Ned to knock him unconscious and carry him out. Aboard a skiff, the three companions witness Vulcania explode. As the Nautilus sinks, Nemo's last words to Aronnax echo: "There is hope for the future. And when the world is ready for a new and better life, all this will someday come to pass ... in God's good time."