Reluctant hero Hiccup Horrendous Haddock III must rescue his best friend, Fishlegs, from the deadly disease Vorpentitis. The only cure is rare and almost impossible to find ... a potato. But where will Hiccup find such a thing?

It's Hiccup's birthday, but that's not going to keep him from getting into trouble. To save his dragon, Toothless, from being banished, Hiccup must sneak into the Meathead Public Library and steal the Viking's most sacred book. But the Vikings see books as a dangerous influence, and keep them locked up and under heavy guard. To save his friend, Hiccup must brave the Hairy Scary Librarian and his dreadful army of Meathead Warriors and face off against...

Hiccup, the reluctant Viking hero, has three months, five days, and six hours to discover America, return to Berk, save his father, battle Polarserpents, and win the annual Inter-Tribal Friendly Swimming Race.

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.