The Viking village of Berk is frequently attacked by dragons stealing livestock and threatening villagers. Hiccup Horrendous Haddock III, the 16-year-old son of chieftain Stoick the Vast, is a misfit who struggles physically but tries to invent mechanical devices to help himself. During a dragon raid, Hiccup shoots down a rare Night Fury dragon but is not believed by others. Determined to prove himself, he searches for the dragon and finds it injured. Instead of killing it, Hiccup frees the dragon, who surprisingly spares him.
Stoick prepares to destroy the dragons’ nest and enrolls Hiccup in a dragon-fighting class with other teens, including Astrid, his crush. Hiccup struggles but befriends the Night Fury, naming him Toothless. He creates a prosthetic tail fin and learns to fly Toothless, discovering dragon behavior that helps him tame other dragons, gaining village attention but also suspicion.
After a fleet attack fails, Hiccup tries to escape with Toothless but is found by Astrid, who witnesses their friendship. Toothless leads them to the dragons’ nest, where they discover the massive Red Death dragon commanding others to feed it. Hiccup and Astrid keep this secret to protect Toothless.
In the final exam, Hiccup attempts to prove dragons can be tamed instead of killed, but a misunderstanding enrages a dragon. Toothless protects Hiccup but is captured. Stoick disowns Hiccup for siding with dragons. Encouraged by Astrid, Hiccup rallies friends and dragons to confront Stoick’s fleet.
In the final battle, they awaken the Red Death, which is defeated through teamwork. Hiccup is injured but saved by Toothless. The village embraces dragons peacefully, and Hiccup, now a hero, begins a relationship with Astrid.