Disobeying Hiccup, the twins follow a retiring Eruptodon to its final resting place, Vanaheim, and learn why no human has ever gone there before.
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.
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.
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.
The gang investigates why Viggo's men are mysteriously shipping marble blocks from a quarry. Next, they try to save two dragons being used as slaves.
After Stormfly tangles with two poisonous Slitherwings while defending Garff, Astrid must risk her own life to get an ingredient to make an antidote.
While trying to stabilize the volcano that threatens to destroy Dragon's edge, the Riders discover troubling evidence of new Hunter activity.
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.
During a trip to Wingmaiden Island to find a Dragon Eye lens, Snotlout challenges Hiccup’s leadership. On another island, an unlikely romance blooms.
