Anna and Elsa head to the enchanted forest outside of Arendelle to discover why a mysterious voice has been calling to Elsa and to stop the enchanted spirits from destroying Arendelle. It turns out that back in the past, there was a battle between Arendelle soldiers and the people of Northuldra who live in the forest, leading to the forest being blocked off from the rest of the world.
Long story short, Anna and Elsa discover that their parents were on their way to Ahtohallan to discover the source of Elsa's power when they were shipwrecked. Anna and Elsa find their parents' ship in the enchanted forest and learn that their mother was Northuldran. What's more, their grandfather was responsible for the conflict and created a dam in the forest that was intended to weaken the Northuldran people. To right the wrongs of the past, Anna realises she needs to break the dam to free the forest.
And she does it just in time. Elsa was frozen in Ahtohallan seeking the voice, which turned out to be a memory of her mother. Elsa becomes the "fifth spirit", the bridge between the magical world and the human world. But, as we all know, a bridge has two sides and Anna is the other one. So, Elsa stays in the forest and Anna becomes Queen of Arendelle, ensuring that the two kingdoms live happily ever after.
