When Dagur the Deranged captures young Gustav, it's up to Hiccup, Toothless and the dragon riders to get him back.

After an attack on Berk, Astrid trains a crew of backup Dragon Riders to battle back—but no one can guess how soon the next strike will hit.

The Skrill returns with a vendetta against Hiccup and Toothless. Hiccup and the Riders must choose a new course of action to stop the vicious dragon.

After getting bad advice from his father, Snotlout tries to seize leadership of the Dragon Riders and starts making reckless decisions on his own.

After months of planning, Hiccup launches an operation to capture the Dragon Eye from Viggo, only to find that someone else has beaten them to it.

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.

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.

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.