Five years have passed since the Vikings and dragons reconciled. While Astrid, Snotlout, and the rest of the gang spend their time competing in the island's popular dragon races, Hiccup and Toothless embark on a journey across the sky, mapping unknown territories. When their adventures lead them to discover a secret ice cave that houses hundreds of previously unseen wild dragons and a mysterious dragon rider, the two friends find themselves at the center of a battle to protect the world.