Handlung

Hiccup (Jay Baruchel) the son of Stoick the Vast (Cate Blanchett) and Valka, and the newly crowned Viking chief of Berk, Toothless (Randy Thom) and their fellow dragon-riders continue to rescue captured dragons in order to bring them to Berk and its bustling dragon and human utopia. Their efforts have resulted in the island becoming overpopulated with dragons. Hiccup has been leading the villagers as chief, but he still doesn't feel that he is the chief his father was.

Gobber (Craig Ferguson) is a seasoned warrior, blacksmith, and dragon dentist. Gobber suggests that Hiccup and Astrid should get married soon, but neither of them feel they are ready in their relationship to take that step. Hiccup's friends include Snotlout (Jonah Hill) a brash, overconfident, and fairly unintelligent but reliable, Fishlegs (Christopher Mintz-Plasse) an enthusiastic friend and knowledgeable in dragon lore, Ruffnut (Kristen Wiig) and Tuffnut (Justin Rupple). Eret (Kit Harington), the former dragon hunter has now joined them.

In a response to the overcrowding, Hiccup desires to find the "Hidden World", a safe haven for dragons spoken of by his late father Stoick (Gerard Butler) late father of Hiccup and Berk's previous chieftain. Hiccup had hoped to find it so that he can end the fighting between vikings and dragons.

Meanwhile, a white female Fury (Randy Thom), held captive by warlords, is given to infamous dragon hunter Grimmel the Grisly (F. Murray Abraham) who is responsible for the near extinction of the Night Furies as bait for him to capture Toothless for the warlords' use as an alpha. The chiefs want control over the dragons and know that all the dragons of Berk will follow Toothless. He decides to use the female Fury as bait to lure Toothless to him, and he doesn't worry about Hiccup since Grimmel sees him as just a boy in over his head.

Toothless discovers the white Fury (dubbed a "Light Fury" by Astrid) in the woods and the two become enchanted with each other until the Light Fury, sensing Hiccup's nearby presence, becomes frightened and flees. Toothless falls in love with the Light Fury, which Hiccup can see. Hiccup and Tuffnut (Justin Rupple) later discover Grimmel's dragon traps in the area which were intended to trap Toothless. He Hiccup brings back a tranquilizer dart they found, which Eret recognizes as Grimmel's work. He warns Hiccup that Grimmel most likely wanted them to find that trap as a means to lead him right back to them.

Grimmel visits Hiccup that night, revealing he has hunted down all the other Night Furies, but Hiccup has prepared an ambush to capture him. However, he summons his acid-spitting Deathgrippers to tear through Hiccup's home. Grimmel escapes, burning down Hiccup's house and part of Berk in the process. In response, Hiccup rallies the citizens and dragons to leave Berk on a quest to find the Hidden World and safety from dragon hunters. This was part of Grimmel's plan all along as he made the Berk's abandon their only position that they could defend and come out in the open ocean. Grimmel plans to keep tracking Toothless with reluctant help from the warlords, all while making more of the venom to tranquilize dragons.

Mid-journey, the Berkians discover an island on which they initially plan to rest for a short while, but the tired Vikings force Hiccup to declare the Island as their new base camp dubbing it "New Berk". The Light Fury reappears later that night, and Toothless goes after her. Hiccup wakes up and goes to try and help him out. Toothless does goofy dances to court the Light Fury, which does not impress her. He then manages to draw her face in the sand, which she seems to like. Unfortunately, she flies away again when she spots Hiccup, and Toothless is unable to fly after her because of his bad fin.

Seeing Toothless's inability to fly solo hindering his growing relationship with the Light Fury, Hiccup builds an automatic tail for him. Upon receiving the tail, Toothless flies off, meeting the Light Fury on his own and flying with her to an unknown land. They take flight together as she demonstrates her ability to camouflage herself using her fire breath. With her help, Toothless is able to use his own power with lightning to achieve the same effect. They continue flying until the Light Fury brings Toothless to a waterfall.

Valka, on a scouting patrol, notices Grimmel's approaching army and quickly reports back to Hiccup. Hiccup and the riders head to capture Grimmel, yet they fall into his trap and barely escape. Ruffnut (Kristen Wiig) is captured but irritates Grimmel until he lets her go and secretly follows her to the Berkians' new location.

Hiccup and Astrid (America Ferrera) who is now Hiccup's betrothed fiance, who are searching for Toothless, find the Hidden World. The Hidden World is after a waterfall at the end of the world, and behind a long-illuminated cave structure. They see Toothless and the Light Fury leading the dragons there, now a happily mated pair. When the two are discovered, Toothless rescues Hiccup and Astrid and returns them to the Berkians, with Hiccup realizing his people would be intruders and unsafe in the Hidden World.

Suddenly, Grimmel appears and captures Toothless and the Light Fury, who followed Toothless back. Toothless's alpha status allows Grimmel to capture the rest of Berk's dragons by threatening to kill the Light Fury if any dragon or Berkian attacks.

Hiccup feels hopeless and sees himself as a failure as chief. Astrid encourages him as she always has, letting him know she was the first person to believe in him and will always be there to pick him up. Hiccup rounds up his friends with their dragon suits to fly after the ship.

With Astrid's encouragement, Hiccup sets out with the dragon riders to stop Grimmel and his army. Gliding on wing suits, they catch Grimmel's army off-guard, igniting a battle. Hiccup frees Toothless, but Grimmel drugs the Light Fury into obeying him. The Deathgrippers fly in and surround Toothless, until he harnesses his lightning power and electrocutes them all before vanishing.

Hiccup and Toothless give chase, but Grimmel tranquilizes Toothless in midair, causing Toothless to fall helplessly towards the ocean. Hiccup, realizing he cannot rescue Toothless alone, frees the Light Fury. Hiccup is hanging on to Light Fury and Grimmel is in-turn hanging on to him. Releasing Light Fury means Hiccup falls to his own death. Hiccup implores her to save Toothless. He then let's go, causing him and Grimmel to fall towards the water as well. Hiccup loosens his peg leg, causing Grimmel to fall to his death, while the Light Fury grabs him and brings him to safety.

Back on the island, Hiccup realizes that dragons will never be safe in the human world. Hiccup bids a tearful farewell to Toothless and all of the Berkians set their dragons free to live in the Hidden World. The other Berkians must then say goodbye to their beloved dragons. Toothless brings all the dragons to his command for one last time as the Light Fury leads them away to their new home. Toothless shares one last look with Hiccup.

The following winter, Hiccup and Astrid marry on the island on which the Berkians have settled. Ten years later, Toothless and the Light Fury are shown to have mated and given birth to three dragon fledglings. Hiccup, Astrid, and their two children sail across the sea and reunite with them at the edge of the Hidden World. Toothless flies over to the boat and does not seem to immediately recognize Hiccup. He slowly moves his hand toward his snout as he did when they first met, and Toothless pounces on Hiccup for the first time in perhaps a decade. Astrid then brings the kids over so that Hiccup can introduce them to Toothless.

Hiccup and Astrid take them flying on Toothless and Stormfly, accompanied by the Light Fury and their offspring. Hiccup vows that Berkians will guard the secret of dragons, until humankind can co-exist peacefully with each other, and dragons can return in peace.