A huge sea monster has attacked and wrecked several ships from beneath the sea. Professor Arronax bravely joins a mission to hunt down the beast. He goes aboard the Nautilus, a secret submarine helmed by the mysterious Captain Nemo.At first, the mission is exciting, as Nemo takes Arronax on a voyage around the underwater world. But when things start to go wrong, Arronax finds there's no escape from the Nautilus. He is now Captain Nemo's captive, 20,000 leagues under the sea!