While hunting for gemstones needed to complete the Dragon Eye 2, Hiccup learns an old friend isn't who he seems. Dagur faces a bully from his past.
Stoick and Hiccup are led on a wild goose chase in search of willow bark for medicine, leaving Berk vulnerable to an enemy attack.
During a trip to Wingmaiden Island to find a Dragon Eye lens, Snotlout challenges Hiccup's leadership. On another island, an unlikely romance blooms.
Upset after learning his ancestors were Hunters who killed off Dramillions, Fishlegs sets out to see if he can find any of the dragon species left.
Hiccup grows wary when Gruffnut arrives on the twins' 19th birthday to administer a Thorston coming-of-age ritual involving three dangerous challenges.
An announcement leads Astrid to question her relationship with Hiccup. The Riders discover an Armorwing that has a Dragon Eye lens welded to its body.
While visiting Wingmaiden Island, a baby Razorwhip bonds with Ruffnut, who suddenly finds herself trying her hand at being a Wingmaiden.
When the Flyers try to hug him because he's no longer useful, Viggo forces Hiccup to help him get revenge by stealing their Dragon Eye and lenses.
After learning Krogan is using a Deathsong to lure and subdue Singetails for his growing army of Flyers, the Riders set out to rescue the dragon.
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.
After learning several Flyers followed Heather to Vanaheim, the Riders must stop them from reporting the sacred island's location to their leader.
With the fifth lens in place, the Dragon Eye 2 unveils the apparent King of Dragons, and Fishlegs immediately knows what it is and where to find it.
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.