Long ago up North on the Island of Berk, the young Viking, Hiccup, wants to join his town's fight against the dragons that continually raid their town. However, his macho father and village leader, Stoik the Vast, will not allow his small, clumsy, but inventive son to do so. Regardless, Hiccup ventures out into battle and downs a mysterious Night Fury dragon with his invention, but can't bring himself to kill it. Instead, Hiccup and the dragon, whom he dubs Toothless, begin a friendship that would open up both their worlds as the observant boy learns that his people have misjudged the species. But even as the two each take flight in their own way, they find that they must fight the destructive ignorance plaguing their world.

It's been five years since Hiccup and Toothless successfully united dragons and vikings on the island of Berk. While Astrid, Snotlout and the rest of the gang are challenging each other to dragon races (the island's new favorite contact sport), the now inseparable pair journey through the skies, charting unmapped territories and exploring new worlds. When one of their adventures leads to the discovery of a secret ice cave that is home to hundreds of new wild dragons and the mysterious Dragon Rider, the two friends find themselves at the center of a battle to protect the peace. Now, Hiccup and Toothless must unite to stand up for what they believe while recognizing that only together do they have the power to change the future of both men and dragons.

When Hiccup discovers Toothless isn't the only Night Fury, he must seek "The Hidden World", a secret Dragon Utopia before a hired tyrant named Grimmel finds it first.