Nemo takes his prisoners on a trip around the world, going through all of the world's oceans. They travel 43,200 miles, or 20,000 leagues (that is why the book is called "Twenty Thousand Leagues Under the Sea"). They have many adventures. But then Arronax discovers that Captain Nemo attacks some ships on purpose, to try to sink them. Nemo is trying to get revenge on a country that killed his family. But he will not say which country it is, or even where he came from.