"A dragon rebellion is coming-filled with the meanest, nastiest dragons in the Archipelago. Razor-wings, Tonguetwisters, and Vampire Ghouldeaths are attaching Vikings and seem to be seeking one soul in particular: Hiccup Horrendous Haddock the Third! Only a King can save them...and only a champion with all of the King's Lost Things can be King. In his adventures, Hiccup has collected quite a few "things" himself. But can a scrawny Viking save the...

It's Hiccup's birthday, but he must save his dragon, Toothless, from being banished. He sneaks into the Meathead Public Library to steal the Vikings' sacred book, but must brave the Hairy Scary Librarian, the army of Meathead Warriors, and the Driller Dragons.

Hiccup, stranded with Toothless on the Beach of the Broken Heart and being hunted by an old enemy, faces Ug the Uglithug, Berserks, and Scarers and tries to save Fishlegs from the Beast.

While Astrid, Snotlout and the rest of the gang are challenging each other to dragon races, Hiccup and Toothless journey through the skies, charting unmapped territories and exploring new worlds. When one of their adventures leads to the discovery of a secret ice cave that is home to hundreds of new wild dragons and the mysterious Dragon Rider, the two friends find themselves at the center of a battle to protect the peace.