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.

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.

During Berk's annual Bork week celebrations, Hiccup is granted access to Bork the Bold's private and personal archives. When he finds information and a map about an island inhabited by Night Furies within Bork's notes, Hiccup is determined to bring Toothless to his family.

Mildew has betrayed the Vikings of Berk and allowed Alvin the Treacherous to kidnap Hiccup and Toothless. Astrid and Stoick must rescue them from Outcast Island along with help from a new friend.

Certain that Alvin is planning an attack on Berk, Stoick institutes flight restrictions on the dragon academy. Hiccup, certain that Alvin will be using his newfound dragon-training knowledge to bolster his attack, forms a secret “Dragon Flight Club” in order to train the kids to defend Berk against Alvin’s dragon army.

A Terrible Terror training competition leads to a heated rivalry between Fishlegs and Snotlout, allowing Alvin to kidnap Meatlug. The kids must use their newly trained Terrors to rescue their friend.

Tuffnut goes undercover to help the riders rescue a Skrill.

Alvin reveals he trained the Screaming Death to attack Berk and destroy the island's inhabitants and only Snotlout and Hookfang can save Berk before it's too late. Meanwhile Hiccup gets ready for a final fight against Dagur to save Toothless and end the barbarians invasion of Berk once and for all.