Five years after the Viking village of Berk made peace with the dragons, they now live among the villagers as helpful companions. Hiccup goes on adventures with his dragon, Toothless, as they discover and map unexplored lands and territories. Having come of age, he is being pressed by his father, Stoick the Vast, to succeed him as the chief, although Hiccup remains unsure if he is ready for this responsibility.
The call to adventure When Hiccup and Astrid are exploring a new place, they find an ice cave that results to be a fort where they meet Eret, who blames them for the destruction of his fort and the dissappearance of his dragons for Drago, the conqueror. Hiccup and Astrid return to Berk in order to warn Stoick about about Drago's dragons army, so Stoick orders the villagers to prepare for battle. Stoick explains that he once met Drago at a gathering of chiefs, where he murders everyone after being mocked for offering the chiefs his services in return for their servitude and total obedience. However, Hiccup refuses to believe that war is imminent, so he wants to go and search for Drago in order to reason with him and stop the war.
Accepting the call Hiccup tells his father that he's going to find Eret so he takes him to see Drago, but Stoick refuses to let him go because it is too dangerous. Hiccup doesn't care about the risk so he flies off with Toothless in search of him.
Entering the unknown During his journey, Hiccup gets captured by Valka, a dragon rider who results to be his mother. She explains that she was unable to kill dragons, so she pretended to be dead and ran away. She has spent 20 years rescuing dragons that were captured by Drago, and bringing them to an island made of ice by the Bewilderbeast, the alpha dragon. In the island, Hiccup sees the majesty of all kinds of dragons being together and in peace, and he also discovers that baby dragons are immune to the alpha's control. Stoick tracks Hiccup to the island and discovers that his wife is alive.
Supernatural aid and helpers Valka shows Hiccup the goodness of dragons and how they can be easily manipulated by the one who's in control. When Stoick dies, Valka encourages Hiccup by saying he's the only one who can unite humans and dragons. Inspired by these words, Hiccup returns to save Berk and stop Drago. Astrid and Hiccup's friends are always supporting him too, so when the time of war comes, they engage in battle alongside him.
Tests & the supreme ordeal Drago and his army approach to Valka's sanctuary, where the battle begins. Hiccup tries to convince Drago to stop the war, but Drago orders him killed as well as Toothless and the rest of the dragons in the sanctuary. Toothless is compelled by Drago's Bewilderbeast to kill Hiccup, but Stoick pushes his son out of the way, dying instantly. After Stoick's funeral, Hiccup returns to battle in order to defeat Drago and save his village. But first, he struggles to recover control of Toothless.
Restoring the world Hiccup manages to get Toothless back. Toothless challenges the alpha and Drago's Bewilderbeast freezes him and Hiccup. However, Toothless melts the ice and reveals himself as the new alpha dragon, so he and the rest of the dragons start shooting fire at Drago and his Bewilderbeast, making them run away and dissappear in the ocean. Peace is restored between dragons and humans, Berk is safe and Hiccup is proclaimed the new chief of the village.