The Evening before Hiccup is taken to be with the dragons, King Agnarr of Arendelle tells a story to his children, Elsa, Hiccup and Anna.
That their grandfather, King Runeard, had established a treaty with a neighboring tribe of Northuldra and a ancient dragon, known as the Foreverwing.
By building a dam in their homeland, the Enchanted Forest, this dam would strengthen their waters.
However, a fight occurs, resulting in Runeard's death, the fight engages the Foreverwing and the elemental spirits of Earth, Fire, Water, and Air of the forest.
The spirits and the Foreverwing disappear, by placing a wall of mist that traps everyone in the Enchanted Forest.
The young Prince Agnarr barely escapes due to the help of an unknown saviour, as a the roar of the Foreverwing and a magical siren echo across the land.
Three years after her coronation and the return of Hiccup, Arrendale celebrates the autumn harvest in the kingdom with Anna, Olaf, Kristoff, Sven, and the dragons.
After the harvest, when the group is playing charades, Elsa hears the magical siren and Hiccup starts to hear the Foreverwing's call.
The two of them follow their magical instincts, but accidentally awaken the spirits and the ancient dragon, forcing everyone in Arrendale to evacuate.
When the Kingdom regroups and Anna finds out why her sister and Hiccup had been so quiet, Grandpabbie and the Bewilderbeast inform them that they must travel north to find the truth about the past.
When they reach the massive wall of mist, Hiccup and Elsa part it with their touch and the group adventure into the Unknown.
When memories and old faces are shown to the Ice Queen and Dragon Prince, the full story of why the forest was concealed is revealed.
Find out what happens in the final chapter of Snow and Fire, as the truth