Dragons are still dragons, and as a result, they are causing mayhem in the Isle of Berk. Stoick is reconsidering allowing the dragons to roam freely on Berk. It is up to Hiccup and his friends to convince Stoick otherwise.

The peace with the dragons has put Gobber out of business, since his job was making weapons to fight dragons. Stoick asks Hiccup to help find a new job for him ... but unfortunately a change of profession does not seem to go well with Gobber.

The dragons unintentionally reduce Berk's food productivity by still scaring the living daylights out of the local livestock, and with the first winter storm coming, the dragon-riding Viking youths of Berk must try and familiarize the local animals with their Dragon companions.

Hiccup finds an injured baby dragon. Toothless does not warm up to the energetic newcomer and the baby's angry mother arrives looking for her lost son.

The Dragons are blamed for vandalism, and Hiccup tries to prove their innocence by forming a night patrol called the "Dragon United Monitoring Brigade" (DUMB), but not in time to prevent the dragons' banishment from the island. Hiccup begins to suspect that Mildew is responsible for the scapegoat.

Hiccup had discovered Mildew framed the dragons but has destroyed all evidence of it, therefore he must prove of their innocence in order to get them back. Meanwhile, Alvin the Treacherous of the Outcast Tribe are on the mission to raid the Isle of Berk in order to find and capture the "Dragon Conqueror".

Stoick is in need of learning how to ride a dragon, and he quickly insists on riding Toothless all the time. Meanwhile, a mysterious dragon has been attacking fishing ships.

After getting his picture painted with his father, Hiccup begins to fear that he is not Stoick's ideal son, so to prove himself, he and his friends set out on a treasure hunt that even Stoick had not been able to complete.

After Mildew poisons all the dragons on the island, he is forced to help Hiccup, Stoick, and Gobber find and capture the ferocious Scauldron in order to get the antidote.

Heather's betrayal to Berk caused the Book of Dragons to fall into Alvin the Treacherous' hands, and Heather's imprisonment on Berk. In order to get the book back from Alvin, Astrid disguises herself as Heather and goes into Outcast Territory. Towards the end of her mission, Astrid learns and confirms Heather's true motives for helping the Outcasts.

Berk's annual festive sporting competition, the Thawfest games, is underway and all the teens are participating with the dragons for the first time in Viking history. Hiccup is determined to finally best Snotlout, who constantly gloats about being the reigning Thawfest champion, but Hiccup's successes begin to make him arrogant and boastful, much to Astrid's displeasure and disappointment.

Sudden lightning storms are endangering the residents of Berk and it is believed Thor is angry at the island. Mildew leads the superstitious villagers into blaming Toothless, "the unholy offspring of lightning and death itself", for the lightning, leaving Hiccup to find the true answers for Thor's sudden destructive anger.

A rogue dragon – a Whispering Death – shows up in Berk, tearing up the village. He's on a mission to find Toothless and settle a score. Despite Hiccup's efforts to help, Toothless insists on facing the dragon alone. But unlike their past battle, Toothless's inability to fly my prove to be his undoing.

When Snotlout and the villagers mistake dragon eggs for gems that bring good fortune, Fishlegs, who is responsible for the eggs' discovery, must take a stand against Snotlout and reunite the eggs with their Changewing mothers before they destroy Berk.

When the dragon riders discover a frozen Skrill, a lightning-powered dragon revered by the Berserkers, they scramble to get it off Berk.