This is about the adventures of Hiccup Horrendous Haddock III, the fourteen-year-old son of aVikingchief, who must capture adragonfor arite of passage. Set on the Island of Berk, a group of 10 youths of the Hooligan tribe are being led by "Gobber the Belch" to perform their firstmilitaryoperation; to catch their own dragon. Those who are not able to catch and train a dragon areexiledfrom the tribe. This military operation has to be done by every Hooligan.
At the eastern coast of the Isle of Berk is an area known as "Wild Dragon Cliff" and among the youths is Hiccup himself, his friend Fishlegs, Tuffnut Jr., Speedifist, and Wartihog, Clueless and both of Hiccup's enemies; Snotlout and Dogsbreath the Duhbrain. Since the early morning, Hiccup had felt ill and felt no better in this snowy area, but Gobber placed Hiccup in charge regardless, much to the dismay of Snotlout and Dogsbreath who refer to Hiccup as "Hiccup the Useless". By using their dragon baskets, each enter the cave to catch their dragon.
Hiccup manages to get a Common or Garden Dragon and is forced to rush out of the cave because Fishleg's allergies caused him to sneeze. His sneeze caused one of the dragons to wake up. However, Hiccup's best friend, Fishlegs, escapes without a dragon. Hiccup doesn't want his friend to be exiled and thus hands him his dragon and runs back in to get another.
With all the dragons awakening, the vikings have no other option but to jump off the cliff and into the sea. On returning to the village, Hiccup notices his dragon is incredibly small. Gobber advises the youths to train their dragons by using theHow to Train Your Dragonbook from the Hooligan Library.
However, the book has only a single page saying, "yell at it; the louder the better." This does not help at all for Hiccup, who can barely yell, so he has to find another way to train his dragon. He first tries yelling, which fails. He then puts together a list of supposed characteristics of dragons that can be used in training. The list also fails and, despite the insistence by Fishlegs that it will not work, he resorts to pampering his dragon.
After a run-in with his father's dragons, Hiccup brings Toothless down to the beach to practice hunting with Horrorcow (Fishleg's dragon). At first Toothless refuses to budge and constantly complains, but Hiccup takes out his list yet again and runs through the drills. After crossing out all the options on the list he resorts toJokes and Riddles Talk, marked, "Only if Desperate!" Toothless agrees to a deal. This includes one joke for every fish caught by Toothless.
Later, on Thor's Thursday, during the final part of the rite of passage, Toothless offends Fireworm (Snotlout's Dragon) and there is a fight between all of the dragons. This means that they have all failed and will be exiled. However, because there is a huge storm coming, Stoick the Vast (the Hooligan Chief, and Hiccup's father) allows them one last night on the island. During the storm, two Sea Dragons are washed up on the shore of the island. The bigger one eats the smaller one, and soon a viking named Badbreath the Gruff discovers them.
Finding that the H.T.T.Y.D. Book's advice, along with Gobber's Viking Strength, is useless, the Vikings all look to Hiccup for advice, on the sole condition that the boys are no longer exiles. Hiccup goes to speak with the Dragon, who calls himself the Green Death. The monster states that he is peaceful, but nevertheless intends to kill the Vikings and the Dragons, because since he will be eaten by worms when he dies, a Singing Supper as he puts it, he decides everyone else should be eaten.
When Hiccup tells the Elders, they all squabble and fight with each other over what to do. Hiccup decides to use this time to gather the boys and their dragons together and come up with a plan; the dragons will carry home-made feather bombs and drop them on the Green Death to give him an asthma attack. Toothless, however, decides not to go along with this, as he thinks the plan is suicide. The other dragons agree, but, they decide to run if they may lose.
The plan seems to be working. A Purple Sea Dragon the boys discovered earlier, and have used the same tactic on, goes to kill the Green Death. The Green Death, however, wins the fight but suffers mortal wounds. In an act of revenge, he swallows Hiccup whole. Hiccup lands on a spear jammed in the monster's throat. When Toothless sees that all the wild and domestic dragons have left, he concludes Hiccup is his only remaining family and saves him by making the Green Death sneeze. Before Hiccup is sneezed out, he jams his helmet into the Green Death's fire-producing orifice.
When the Green Death tries to breathe fire, the pressure builds up and he explodes. A singing sound is then heard.
Three days pass and Hiccup wakes up to find that Toothless has "died" from his wounds. Hiccup correctly guesses he is only in a coma and goes to save him from having a traditional Viking Funeral, which involves being burnt. Because of his bravery, Stoick proudly calls his son "Hiccup the Useful."