When Tuffnut learns of the deception, Gruffnut takes his place and tries to secretly bring Barf and Belch to the Hunters, but Ruffnut recognizes him and Tuffnut defeats him in battle. Worried, the Riders quickly check on Garffiljorg while the others take the injured Singetail back to the Edge for recovery. The trapped Bewilderbeast, with its ability to control other dragons, calls for help from all available dragons, among them are Garffiljorg, the Eruptodon, the Screaming Death, the Frozen Skrill, Thornado, Bing, Bam and Boom and every dragon the Riders ever encountered. Heather seems to instantly fit in with the riders, but Windshear, used to being Heather's sole protector, complicates things when she acts extremely hostile towards the other dragons as they help with the yearly Nadder Migration. But when Alvin, the villainous leader of Outcast Island and Berk's greatest enemy, decides to attack the island, Hiccup must protect his friends and prevent Alvin from learning the secrets of dragon training. Following him, the riders find that he has mated with a female Monstrous Nightmare. When the dragon riders discover a frozen Skrill, a lightning-powered dragon revered by the Berserkers, they scramble to get it off Berk.
Using a Skrill as a diversion, Hiccup and Viggo enter their headquarters where Viggo betrays Hiccup to earn favor with Johann and Krogan once more. While following the wounded Singetail to the same island, Fishlegs find a hatchery of Singetail eggs and realizes that the Flyers are breeding Singetails. Hiccup reluctantly lets Viggo leave with the Buffalord in exchange for the cure, but as soon as his ship leaves it fights back forcing the Hunters to release it. It is only the Night Terrors forming the shape of the Fireworm Queen that gets the Fireworms to leave the island. Sullivan John Tellegen February 16, 2018 2018-02-16 After learning his ancestors were dragon hunters who killed off the Dramillions, Fishlegs sets out to Dramillion Island with Astrid against Hiccups wishes to find and help protect the Dramillions from harm. Hiccup, Snotlout and Johann try to devise a plan when Fishlegs ends up held hostage by them. Later, an injured Heather and Windshear return from Vanaheim with dire news.
Between this and Hiccup's disappointment, a despondent Fishlegs leaves and discovers a cavern filled with an abandoned colony of albino Night Terrors. Fishlegs believes he has found the perfect candidate, but it turns out to be home to Slitherwings, venomous serpentine dragons that poison Stormfly as she defends Garff to trigger strange wild behavior. The dragon riders fight off the Changewings and free the leader. Though still doubtful, Hiccup and the others scramble to keep the siblings from noticing each other by sending Heather away while offering Dagur a Gronckle he names Shattermaster to get him to leave, but they cross paths anyway. Soon they get a stomach ache and return to Berk to get Meatlug checked by Gobber.
Working together with the Gronkles and Quakens of Dark Deep, the Riders manage to stabilize the volcano, and decide to hold off on returning home to stop the Hunters once and for all. Hiccup allows himself to stand trial and face their punishments, seeing Mala and her tribe as potential allies in their struggles against the hunters and eventually wins her trust. In the end the group is forced to abandon Dragon's Edge and seek shelter with the Defenders of the Wing, where Hiccup resolves to regain the others' trust after it is revealed he is building a new Dragon Eye, while Viggo attempts to reclaim the original one from the Edge's volcano. Continuing his ruse as their ally, Johann suggests taking a trip to the Northern Market with Hiccup alone and that he bring both his Dragon Eye 2 and all of his lenses. Hiccup wants to take the chance to enact revenge on Viggo for his underhanded attack on Berk without a plan, but is caught up investigating and surviving the aggression of a small pack of new dragons and their leader that have driven the Hunters from their observation post.
Meanwhile, Fishlegs discovers Dragon Root, which could end up affecting not just Stormfly and Hookfang, but all their dragons. Before setting out, he remembers his dragon scouts are coming and leaves the twins to look after them. Dagur fires a boulder, from a catapult, onto The Reaper causing the ship to sink, leaving Hiccup with a choice: Retrieve the device he found from Dagur, or save his friends from certain death. Heather, Fishlegs, and Dagur face difficulty saving them due to Viggo's dragon-proof ships until Heather and Dagur work together to take down the fleet. The group mostly welcomes her back with open arms, but Hiccup is suspicious of her new, more aggressive behavior.
Hiccup manages to match Viggo's wit and free the Flightmare and Heather with unexpected help from Dagur, but once again Viggo turns the tables and manages to snatch away the Dragon Eye. As the divided riders struggle against the Crasher's detonative mucus ability, the Queen guides Snotlout and Hookfang to her hive, revealing she needs help defending her babies. Dagur offers her the chance to join with the Berserkers, but she refuses. Using the baby Razorwhips, the Wingmaidens defeat Flyers. . Johann smuggles in the other riders with his ship, but though they infiltrate successfully, they are discovered and imprisoned in the caverns while their dragons are put on auction, beginning with Toothless.
Meanwhile, Krogan and Viggo obtain the lens, setting the true mastermind behind the Hunters, Johann, one step closer to finding the King of Dragons. With the aid of Stoick and the Rumblehorn, the riders create a wall to block the wave and protect the island. In the cave, Hiccups finds Garff while Fishlegs brings the Cavern Crasher to help dig a new exit and move the Singetail eggs to safety. Astrid is cured and the riders offer words for the deceased sailors. After the twins throw everyone in the 'dungeon' they realise they need the other riders to stop the island becoming a pile of ash. Because their slow speed had previously allowed an Outcast boat to escape, Fishlegs decides that producing Gronckle Iron is a more helpful task than flying with the other teens, until Meatlug ends up ingesting a magnetic rock, attracting all the metal in the village-including Hiccup's metal leg. One baby ends up choosing Ruffnut, whom Atali insists must become a Wingmaiden.
Hiccup and Fishlegs face continuous difficulties working together to deliver the egg, and things are made worse when a pack of wild Fire Terrors inhabiting the cave kidnap the egg. They eventually learn the Quaken's behavior was out of loneliness and defensive instinct, and allow it to remain and share the island with the Gronckles. Fishlegs manages to free the Quakens just as their poundings cause the island to sink and have them destroy the Hunters' stone base. Hiccup must find Toothless and reason with him before the rivalry turns fatal. Hiccup is captured by Ryker and Dagur but is rescued by Barf and Belch who in turn are rescued from drowning by the twins, repaying the debt and returning everything to normal. Convinced that Hookfang has reverted to his old feral nature, Snotlout decides to resign from being a dragon rider.