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.

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.

Hiccup discovers that the town's water shortage has been caused by the Outcasts' plan to hide Whispering Death eggs under Berk, which soon hatch and tunnel under the island, threatening the villagers.

While searching for traps, Tuffnut, Barf and Belch get trapped themselves... and a forest fire is approaching.

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.

Tuffnut goes undercover to help the riders rescue a Skrill.

Dagur the Deranged visits Berk to renew a peace treaty between the Berserkers and Berk, and the dragons are put into hiding to dispel rumours that Berk is training a dragon army. But when Ruffnut and Tuffnut begin to fight, their dragon, Barf and Belch, is left out of control. The Viking youths must bring the twins back together to control their dragon and avoid provoking Dagur to war.

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.

The kids go on a dragon survival-training mission to Dragon Island, where they encounter Dagur, the Berserker Chief, who has become obsessed with hunting the Night Fury.

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.

Hookfang and Stormfly quarrel while the town prepares for the harvest.

Hiccup must help Astrid face her fear of the terrifying Flightmare, a ghostly dragon that seemingly "froze" her uncle with fear, shaming her family name. With Fishlegs' help, they discover that there's more to the Flightmare than meets the eye

When three adolescent Thunderdrums attack the village, only Stoick's Thornado can bring chaos to order.

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.

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.

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.

Snotlout becomes convinced he is dying, and leaves Hookfang to Gustav. But when he "miraculously" recovers, Snotlout takes his dragon back, and Gustav decides to get a dragon of his own and join the academy... whether they want him or not.

Hookfang is losing his ability to catch on fire, and it's up to Snotlout, Hiccup and the others to find the lair of the Fireworm Queen, which may hold the only possible cure, before it's too late.

Hiccup and co. discover an injured Scauldron on the shores of Changewing Island. The kids must heal the dragon and return him safely to the ocean, before he falls victim to the elements, as well as the territorial Changewings.

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.

Berk has been plagued with a bad case of the Eel Pox. Hiccup, Toothless and the gang, along with Gothi, go gather the ingredients for the cure. There's just one problem; the final ingredient is an eel from Eel Island.

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.

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.