Five years have passed since Hiccup and Toothless united the dragons and Vikings of Berk. Now, they spend their time charting unmapped territories. During one of their adventures, the pair discover a secret cave that houses hundreds of wild dragons -- and a mysterious dragon rider. Hiccup and Toothless find themselves at the center of a battle to protect Berk from a power-hungry warrior.

As the son of a Viking leader on the cusp of manhood, shy Hiccup Horrendous Haddock III faces a rite of passage: he must kill a dragon to prove his warrior mettle. But after downing a feared dragon, he realizes that he no longer wants to destroy it, and instead befriends the beast – which he names Toothless – much to the chagrin of his warrior father.

As Hiccup fulfills his dream of creating a peaceful dragon utopia, Toothless’ discovery of an untamed, elusive mate draws the Night Fury away. When danger mounts at home and Hiccup’s reign as village chief is tested, both dragon and rider must make impossible decisions to save their kind.