Fishlegs and Meatlug begin an annual dragon census of the island. While counting the resting Night Terrors, a stray Fireworm suddenly lands on his map and burns through a hole. Fishlegs suspect the Fireworm just got lost, but later on more and more Fireworms begin appearing on the island, and each time they land they burn something.
The Riders are informed and suspect the Fireworms may be migrating, Fishlegs informs them that Fireworms do not migrate whole but first have to sent scouts to check islands that act as their stop-over, if the scouting Fireworms find it suitable for rest then the rest of the Fireworms may be here in a week. Snotlout decides to abandon and let the island burn to the ground, Hiccup refuses this and suggests they set up precautions to protect the island from burning.
At the Clubhouse, the Riders have done their work of bringing the supplies needed to prevent an inferno set by the Fireworms while Fishlegs have found a perfect evacuation site for the Night Terrors in a cave high and desolate enough to prevent the Fireworms from getting near them. The Riders await the twins' return to find out what useful they've done, which the others are certain they've done nothing. On the contrary, the Twins return claiming they've done something but in no relation with the Fireworm situation, they inform them that they have found something 'awesome' and invites them to it.
When they arrived, the Twins have found what they call their "Namey Rock", where actually Fishlegs identifies it as a claim stone. Hiccup reads the claim, which says that Magmar Thorston, the Twins' long-lost great uncle, proclaimed his discovery of the island, and claimed it in his name and his families', meaning that ownership shall be passed onto each member of the Thorston clan forever and ever. Though Snotlout refuses to believe as it might be fake, Fishlegs however observes the stone to be legit as for one thing, all the spelling used is correct.
Hiccup sends for Gobber and Stoick to authenticate the stone for an official conclusion whether the Twins are truly the rightful owners of the island or not. In the end, Gobber observes the stone to be 100% authentic. As a result, Stoick has no choice but to go with Viking law and as current Chief of Berk, dubs the Twins the official owners of the island. Hiccup pleads his father to rethink his decision, but as he can do nothing about it Stoick laughingly refuses and leaves as the two men continue to chuckle.
The Riders cannot accept what just happened, Snotlout recommends they just kill them, however, Hiccup suggests they let them be the rulers. Other than the fact that legally, they don't have a choice in the matter, he is certain that eventually they'll realize how hard leadership is. The Riders reluctantly accept the experiment, meanwhile, more of the Fireworms begin landing on the island and are creating a small blaze of fire.
Afterwards, the Twins has now named the island to be Thorstonton as they begin placing a sign above the clubhouse doorway. Next, Tuffnut begins to push forward with their agenda instead of fireproofing the island, he calls the others join them in a gathering to give out their job assignments. Fishlegs is assigned to be the Twins' Poet Laureate despite they not knowing of what that means whatsoever, Astrid is assigned to be the official Royal Brush Clearer, Astrid responds angrily to that but Hiccup tells her to calm down. Snotlout is assigned to be the Twins' Sargent-at-Arms to enforce the laws of the Twins and punish those who don't follow by putting them in their new fancy dungeon, while Hiccup is assigned to be the Twins' stable boy which he is reluctant to accept.
The Twins also give out their rules. (1-2) All must bow to their rulers whenever they enter, remain or exit the room they are present in, basically just bowing all the time. (3) There will be a small fee to give whenever their dragons land or take off, a fee for sleeping, waking up, eating, drinking and even breathing as Astrid sarcastically suggested. (4) The Twins disband the letter 'S' from the alphabet, forbidding anyone to say words that has the letter 'S' in, that would later cause confusion and hard-to speak language. Hiccup asks for any more rules, but when the Twins grab their next list of rules, a Fireworm burns it and the Twins order Hiccup to get rid of it. Hiccup begins to worry and reminds the Riders to keep in touch with the Fireworm situation.
While doing their ridiculous tasks, the Riders are annoyed by the Twins crazy totalitarian leadership, where they send Astrid to the dungeon with the help of their sargent-at-arms after Astrid ridicules and disrespect their laws. Fishlegs is then later on sent to the dungeon for failing to amuse Tuffnut's chicken with his poem. Meanwhile, the full migration of the Fireworms arrive on the island and almost immediately begins to burn the land they cover. With Astrid and Fishlegs in jail they worry that danger is getting closer by the minute and Hiccup is their only hope to convince the Twins to deal with the situation.
As the Twins and Hiccup fly throughout the island, where Hiccup thinks they are concerned with all the destruction, in reality they are only searching for a good place to build their summer home, and Ruffnut finds a good spot once all the Fireworms clear the area. The Twins asks Hiccup for any consideration, Hiccup first informs them to realize that if they throw everyone in jail there will be no one left to build their Summer Palace, and second is to make them realize that without any help from the others, Thorstonton will burn to the ground. The Twins sees that Hiccup has a point however the Twins discover that he's breaking the law as Toothless is flying as fast as Barf and Belch.
Consequently, they are both thrown into jail, and Snotlout is forced to throw himself in jail shortly after, claiming that he was 'framed'. The Riders have had enough and demand that they break out but Hiccup calms them down reassuring them that the Twins can't be that oblivious to the mayhem ensuing. Meanwhile, the Twins continue playing, but they finally realize the warnings Hiccup and the Riders was telling all day, the Fireworms are now closing in on the clubhouse and the Twins instead continues to blame each other.
At the dungeon, Hiccup has finally had enough and decides to break free, he orders Toothless to shoot down the gate, but at the last moment, Tuffnut appears begging for help. Hiccup and the Riders ask them humorously if they can still save their island by themselves, the Twins confess that they can't and offers them freedom but still orders them to come help them put out the fires. However, the Riders cannot as they are just 'following their rules' and it'd be total anarchy not to follow. The Twins desperately begs for their help and asks if there's anything they desire.
The Twins offer them to be some 2nd class rulers, but Hiccup demands the island to be shared equally, meaning there are no rulers to dictate laws of their own. Tuffnut sees it as blasphemous and refuses to accept, but quickly changes his mind when the Fireworms are now inside the dungeon as well.
The Riders attempt numerous efforts of rerouting all of the Fireworms, such as assaulting them and creating a strip of dirt that they claim will prevent the fire from expanding. However, all such attempts fail as the intense heat and smoke is too much for the Riders. Hiccup decides that they wait it out in the cave where the Night Terrors are in, unfortunately, Fishlegs arrives informing that he can't find a single Night Terror meaning that they've all fled. The Riders begin to suggests that they abandon the island, however Tuffnut, having a change of heart, refuses to give their now equally-shared island. However that might be impossible to do, as the Riders witnesses a Fireworm Queen heading their way and all are in favor of bailing, but Snotlout sees it to be not the Fireworm Queen but the Night Terrors, imitating it's shape.
Hiccup and Toothless seizes the opportunity, they get the Terrors' attention by drawing them to sea, with the Fireworms fooled and follows their 'Queen'. Hiccup leads them to a rocky island where it is impossible to burn, when the Terrors land they scatter but the Fireworms are rerouted otherwise and made the rocky island their new stop-over.
The next day, the Twins are upset of giving up of being rulers of the island but Hiccup tells them they did the right thing and hoped they learned something. The Twins did learn something, learning that leadership 'blows', but are satisfied of having their own claim stone in memory of their glorious reign over the island. However, Meatlug devours it and turns it into lava, the Twins are disgusted.
With the claim stone, the only piece of evidence of the Twins' ownership of the island, gone, Snotlout cheers and sings happily as the island is for everyone again and the rest of the Riders also join along as they dance and sing in joy for equality.
- Dragon's Edge had been claimed by Ruffnut and Tuffnut's great uncle, making them the owners.
- The island is re-distributed among the riders at the end of the episode.
- The title is similar to the movie "Reign of fire".
- When Tuffnut informs Hiccup he is the new stable boy, the page he is reading from actually translates to the beginning of President Abraham Lincoln's Gettysburg Address.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Nolan North as Stoick the Vast
- Chris Edgerly as Gobber the Belch
- Christopher Mintz-Plasse as Fishlegs Ingerman
- Andree Vermeulen as Ruffnut Thorston
- T.J. Miller as Tuffnut Thorston
- Zack Pearlman as Snotlout Jorgenson