The Riders race to the home of the true King of Dragons. But the Flyers are already there, and they soon come face to face with the legendary creature.
While on night patrol, Stoick is ambushed by the Flyers and gravely injured, leaving Hiccup torn between his duties as a son and as the Riders' leader.
Hiccup grows wary when Gruffnut arrives on the twins' 19th birthday to administer a Thorston coming-of-age ritual involving three dangerous challenges.