In the aftermath of the events of the movie, the kids are enjoying their new lives with dragons, but the rest of the villagers aren't so sure. Hiccup and his friends have to find a way to train the dragons to live in peace with the rest of Berk.

Now that the dragons have assimilated into Berk, just about everyone seems to be better off. Except for Gobber, who made a career of building weapons to fight the dragons. Hiccup takes it upon himself to find a new role for Gobber in the new dragon-friendly village.

While out flying on their dragons, the kids stumble upon a small dragon with an injured leg. They bring it back to Berk - no one has ever seen this species before, and everyone loves the new dragon, even Stoick, who names him Torch. Everyone but Toothless, that is, who knows that Torch is the offspring of the deadly Typhoomerang, who is heading towards Berk in search of her missing baby.

When the dragons are blamed for a series of damages around the village, Hiccup and the kids form the Dragon United Monitoring Brigade (aka DUMB). But when the Great Hall is ravaged, Hiccup suspects that someone else might be framing the dragons, in order to get rid of them.

After the dragons are banished from the island, Hiccup searches for evidence to prove their innocence. 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.