Erik Hellstrom, believing himself to be the Norse god Odin, stole an ancient spear called the Gungnir, presumably an artifact of Atlantean origin. When Milo, Kida, Audrey Ramirez, Vincenzo Santorini, Gaetan Moliére, and Obby track Hellstrom down in the frigid Nordic Mountains, he presumes Kida to be his long lost daughter and kidnaps her. His intentions are to end the world in Ragnarok. He creates a lava beast and then an ice beast to destroy the world, but well-placed explosives used by Vinny distract the monsters long enough for Kida to retrieve the spear and vanquish the beasts.
Having retrieved the spear, Kida realizes her father was wrong to hide the Crystal from mankind. She combines the Spear with the Heart Crystal and lifts Atlantis to the surface. In the end, we see Atlantis above the water for the first time in over nine-thousand years. From then on, the world was a better place.