Searching for a sea monster, a scientist discovers an amazing underwater vessel. At first he's thrilled to be invited aboard the Nautilus. What changes his mind? He discovers that the mad captain plans to stay at sea forever. A deadly and huge sea monster is sinking ships. Three men--a French scientist, his trusty sidekick, and a Canadian harpoonist are thrown from the deck of their American warship. A door opens on the side of the monster, and they are taken inside the greatest submarine in the world, the top-secret Nautilus commanded by a madman who will take them 20,000 leagues into the depths