The movie begins with Hiccup, now 20 years old, exploring the world outside the island of Berk with Toothless. He creates detailed maps of the area, while Toothless enjoys flying and playing with his owner. Meanwhile, on Berk, the villagers are holding a dragon race, with Astrid winning first place.
However, during one of Hiccup's explorations, he and Toothless stumble upon a group of dragon trappers led by Eret, who works for the notorious dragon hunter Drago Bludvist. Eret tries to capture Toothless, but fails, and is instead captured by Hiccup and his friends.
Hiccup tells his father, Stoick the Vast, about the trappers and reveals his findings of a large ice cave full of dragons. Stoick tells Hiccup that they must prepare to defend Berk against Drago and his army, who are also seeking the dragons.
Hiccup, who was once skeptical of the idea of a Dragon Rider, decides to find the person rumored to ride the dragons from within the ice cave. His journey leads him to Valka, his long-lost mother, who has been living in the hidden cave for the past 20 years and has been rescuing dragons from Drago.
Hiccup reunites with his mother and discovers that she has been working on a way to save all dragons from enslavement. At the same time, Drago arrives with his army and tries to convince Hiccup and Stoick to join his cause, but they refuse.
As Drago attacks Berk, Hiccup and his friends mount their dragons and engage in a heated battle against Drago's forces. During the fight, Stoick is killed by Drago, leaving Hiccup devastated.
Hiccup later confronts Drago, telling him that he cannot control the dragons, as they are intelligent creatures with their own free will. Toothless, under the influence of a dragon controlling device created by Drago, attacks Hiccup, but Valka and the rest of Berk's dragons break free from their chains and fly to attack Drago's army.
Toothless and Hiccup eventually reunite, and together, they destroy Drago's dragon-controlling device. The evil villain is defeated, and Berk is saved.
The movie ends on a bittersweet note as Hiccup, after losing his father, is now forced to become the Chief of Berk and lead his people into the future.
