20,000 Leagues Under the Sea by Jules Verne

There is a sea monster which is haunting sailors and taking away the lives of great men. The people of a small town have had enough of it and have decided to send a few good sailors to destroy the ghastly beast. But it turns that the beast isn't actually alive, or so the Professor and the ships best harpooner Ned find out when they are thrown overboard. The beast is what seems to be a large submarine. The captain of the Nautilus is called Captain Nemo. He welcomes them on board but the next day keeps them as prisoners. Ned has planned to escape but Captain  Nemo has other intentions...