Hiccup believed he could change the mind of Drago Bludvist and show the madman the truth about dragons. He was wrong. Now, Hiccup Horrendous Haddock III is the last Viking in the world, thanks to Drago Bludvist and his Northern Alliance. With nothing left to lose, Hiccup embarks on a quest to exact revenge on the man that put his loved ones and people to the sword.

With the dragons now in the Hidden World, Hiccup and his wife, Astrid lead New Berk into a new era of peace. However, an old friend returns to not only live among the Hairy Hooligans but also to confess her feelings toward the chief and chieftess of New Berk. Not only that, but a new threat encroaches into Scandinavia to wage war on the Vikings and to take the dragons.

Leaving Eret's ship in search of Drago, Hiccup and Toothless stumble upon a mysterious dragon rider and Stormcutter who take them back to their home. Once there, Hiccup learns that this dragon rider is in fact his long lost mother. They meet, they bond, and then things take a rather… unexpected turn.