While trying to stabilize the volcano that threatens to destroy Dragon's edge, the Riders discover troubling evidence of new Hunter activity.
As the Riders investigate why traders are disappearing from Northern Markets, Hiccup and Snotlout fall victim to a treasure-hoarding dragon.
The Riders accept an invite to Berserker Island, where their reunion with Heather, Dagur and a young familiar face is interrupted by a sudden revolt.
When SnotLout is rescued from a storm by a tribe of winged women, he thinks he's gone to Valhalla - until he learns he's going to be their dinner.
Disobeying Hiccup, the twins follow a retiring Eruptodon to its final resting place, Vanaheim, and learn why no human has ever gone there before.
When a pair of outcasts visits the Edge seeking the help of Thor Bonecrusher, Fishlegs allows Snotlout to hypnotize him to evoke his mighty alter ego.
After the Edge is ambushed by a group of Singetails, the Riders quickly take flight to ward them off, but are shocked when they get a closer look.
The Riders flee to Berk, where Stoick's plan for defeating the Flyers, which will require a painful sacrifice, spurs Hiccup to seek an alternative.
An unlikely ally helps Hiccup uncover Singetail behaviors that can be exploited to conquer the Flyers. An overconfident Krogan makes a strategy error.
After Stormfly tangles with two poisonous Slitherwings while defending Garff, Astrid must risk her own life to get an ingredient to make an antidote.
When Ruffnut refuses to become Throk's bride because it would mean leaving her twin, Tuffnut fakes his own death to give her the freedom to marry.
A sketch in an old diary leads Hiccup and Fishlegs back to Vanaheim, where they help Dagur search for his long-missing father, Oswald the Agreeable.
When Heather goes to meet a man claiming to have seen Oswald, she walks into a trap that forces the Dragon Riders to pay a dear and unexpected price.