Zgodba nas popelje v mitični svet Vikingov in zmajev, na Otok gumpcev, kjer živi tudi najstnik Viki. Spopadi z zmaji so tukaj nekaj normalnega, bojevitost pa je nujno potrebna lastnost vsakega Vikinga. Viki nima smisla za kaj takega, poleg tega se tudi zaradi svojega čudnega smisla za humor in naprednih pogledov na svet težko ujame z drugimi vaščani. Čeprav je sin poglavarja, ga vsi gledajo postrani. Ko se Viki skupaj z vrstniki začne uriti za boje z zmaji, se mu ponudi priložnost, da se dokaže kot pravi borec. Potem pa sreča ranjenega zmaja in se z njim spoprijatelji.
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.