Hiccup is now into adulthood, young but now the leader among the Dragon-rescuing Vikings of their island fortress village of Berk. Though the Vikings have lived in Berk for generations, Hiccup soon sees that they’ve outgrown their small island, especially with the overcrowding of the Dragons there as they rescue more of them, eyeing the mythical sanctuary on the edge of the world to guide these magical beasts. Meanwhile, love may be in the air, with Hiccup perhaps on the verge of marriage with Astrid, though she seems reticent, and Toothless perhaps finding a mate with a female Dragon very much like him, dubbed a “Light Fury” due to its alabaster color, in contrast to Toothless’ obsidian appearance. Unfortunately, it’s all a trap set by Grimmel, the notorious hunter of Night Fury dragons, who aims to snuff them all out at any cost.
Mackenzie Foy stars as Clara, suffering through grief with her father and two siblings during their first holiday without her recently deceased mother, Marie. Clara receives an enigmatic and ornate Christmas gift, the last from her mother, a metallic contraption shaped like an egg with an elaborate keyhole that came with no key that might fit accompanying it. She is despondent that she cannot open it without ruining it, and it causes her to be depressed during the big holiday gala put on by her godfather, Drosselmeyer (Morgan Freeman). who, it turns out, had created the egg for her mother. During the events of the evening at Drosselmeyer’s mansion, she follows a string that will lead to Drosselmeyer’s own gift to her, way out from the party and into another dimension, to a mystical and magic-fueled world called the Four Realms.