When an eerie red glow appears, the giant eel suddenly releases the Nautilus, it turns out to be a chain of underwater volcanoes. Without steering power, the Nautilus continues to sink towards the dangerous lava - and it soon becomes clear that only Humility can save the crew.

The underwater volcanoes turn out to reveal a clue to the legendary underwater city of Atlantis. A small group goes exploring and finds what appears to be an ancient outpost of the lost civilization, but also realizes that it is home to terrifying sea lilies and the crew must fight for their lives.

A daring battle between the Company ships Dreadnought and Nautilus leaves both stranded in the Arctic ice, leading to an uneasy truce. Nemo reunites with a friend from his past and is shaken by more revelations about his father.