As the Riders are performing a training exercise, Snotlout has been hardly pushing his dragon training non-stop, the Riders express their concern and recommends rest for Hookfang but Snotlout justifies it by saying that 'Rest is for the weak' and he pushes on.
When they perform an exercise where Astrid volunteers as an enemy dragon-flying Outcast, the rest of the Riders must avoid her from being tagged or they are out of the drill. Astrid manages to tag out Fishlegs, and the Twins, but fails to tag out Hiccup. When she finds Snotlout she dives near him, Snotlout orders Hookfang to reignite himself in flames, but shockingly he unables to do so and appears to barely even look in good condition.
The Riders halt their exercise as they observed Hookfang unable to flame up earlier and request Snotlout to let them check his dragon's health, Snotlout reluctantly approves but is confident that Hookfang is fine.
At the Academy, Hookfang's condition worsens as he is completely unable to produce flames, has a pale color skin, and flaking scales. Fishlegs sees the condition critical, as he explains a Stoker class dragon such as a Monstrous Nightmare, can eventually lose it's ability to flame, and in Hookfang's case he is loosing his flame due to being pushed too hard by Snotlout. Snotlout sees that he's only 'a little low on flame' and asks Fishlegs the cure, however, Fishlegs responds that they have to figure it out at once before Hookfang completely looses his ability to flame up as he'll eventually die out.
At Night, Snotlout takes care of his dragon back home and tries to inspire him that he's an invincible dragon like him. Spitelout arrives asking for his bludgeon's whereabouts, Snotlout lets his father have he's as Spitelout is having a competition of which head is the strongest. As he is about to leave, Spitelout notices his son's dragon's condition and gives him a piece of advice about their 'sword' that if it's 'not working properly' they 'sharpen' them, however, if they 'cannot be sharpened any longer' they'll have to 'get a new sword'. Snotlout is deeply depressed hearing that and sits next to Hookfang's side to comfort him.
The next day at the Academy, Hookfang's condition worsens as he can barely move and Snotlout is upset though he covers it up that it's just the 'dusts' to avoid being teased by the Twins. After researching Bork's documents, Fishlegs discovers a document containing how to reignite a Stoker class dragon's flame, he shows Hiccup an image of a Monstrous Nightmare surrounded by Fireworm dragons or Flame Eaters by Bork. Hiccup,Astrid and the Twins travel through Berk to round up as many Fireworms as they can, while Fishlegs keeps reading and Snotlout comforts his dragon.
After rounding them up, they first put the fireworms around Hookfang, but nothing happens, they then put the fireworms on Hookfang himself so that he can directly absorb the Fireworms' heat. It's beginning to work effectively, but it's not enough to reignite Hookfang completely. Snotlout desperately requests more Fireworms, but sadly, Astrid informs him that's all the Fireworms on Berk.
Suddenly, the Twins are playing with the fireworms, Hiccup discovers that their stupidity has gave him an idea, he demonstrates that when they put Fireworms near each other, their skin gets brighter and hotter, the Twins are impressed by themselves after discovering that. Using the idea, Hiccup devises a plan to find more Fireworms on Fireworm Island, and to navigate their way Hiccup uses a lamp with Fireworms while using their discovery.
Snotlout tries to motivate Hookfang to use every pocket of strength he has left to fly and join the Riders. Later, the Riders travel throughout the archipelago, however, Hookfang is loosing strength fast and also altitude. Hiccup decides to turn back much to Snotlout's dismay, but when they are about to head back, the lamp glows brighter and discovers they are going towards the right path towards Fireworm island.
They land near a den, Hiccup recommends that Snotlout stay with his dragon and let him and Astrid find the Fireworms, but Snotlout confesses that it was his fault that did this to Hookfang and decides it's his responsibility to fix that, Astrid, Fishlegs, and the Twins stay behind as Hiccup and Snotlout continues and approaches the den.
What they find inside shocks them, they find a huge Fireworm nest where they figure out what Bork meant of the name 'flame eaters', they find fireworms feeding on combs with gel that refuels their heat. Hiccup warns Snotlout to not disturb the nest by grabbing one of the combs, but Snotlout disobeys and grabs a gel-filled comb. Consequently, they disturbed the enormous Fireworm Queen, Hiccup requests that Snotlout return the comb immediately, but he refuses as it's the only thing that can save his dragon.
Snotlout attempts to evade the Fieworm Queen on foot and he is chased, nearly devoured, Hiccup manages to rescue him and they hurriedly leaves the den. Their exit is blocked as the Fireworm Queen confronts them just outside the exit, but Astrid and the others fend the dragon off. Snotlout gives Hookfang the comb that he requests Hookfang must eat immediately.
The Fireworm Queen nears Snotlout and Hookfang. Snotlout confidently confronts the dragon saying that if the Fireworm Queen wants to retrieve the comb it has to take Snotlout down first, willing to lay down his life for Hookfang. Hookfang does not want to see his Rider give up his life for him so he throws the comb away, Snotlout wonders why, Hiccup explains that Hookfang is protecting him.
Despite retrieving the comb, the Fireworm Queen lifts Hookfang up with it's tail, and painfully injecting Hookfang with a special-type of venom with it's tongue. Snotlout sees that his dragon is assaulted and attempts to help him but gets wack by it's wing. Toothless tries to quiet and back down the Fireworm Queen.
When it slowly walks away, Snotlout approaches to his dragon in sorrow and looks as it seems that Hookfang has passed away. Snotlout comforts him saying that he's not just another 'sword', but when he touches his skin, it starts to feel very hot. It's actually revealed, that due to the venom injected on Hookfang, it makes Hookfang's skin and flame to go back to normal, discovering that the Fireworm Queen actually save Hookfang's life and the Fireworm Queen returns back to the nest.
Snotlout weeps in joy but still claims that it's just 'dust' again. The next day, the Riders are waiting for Snotlout and Hookfang to arrive. When they come, Snotlout informs Hiccup that he and Hookfang decide to skip their training as Snotlout wants Hookfang to rest for a while and go easy on his training, by having a stroll around the island with just the two of them, to make sure his in good condition. Jokingly though, Hookfang highly lifts Snotlout into the air and catches him while flaming up and he does it in joy revealing Hookfang made a full recovery.
Seeing that the two are back to their old-selves, the rest of the Riders press on after another job well done.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid
- Christopher Mintz-Plasse as Fishlegs Ingerman
- T.J. Miller as Tuffnut
- Zack Pearlman as Snotlout
- David Tennaat as Spitelout Jorgenson
- Julie Marcus as Ruffnut
- The title comes from Race to Witch Mountain.
- Hiccup does not use his shield in this episode.
- Both Stoick and Gobber don't appear in the episode.
- The page in the Dragon Manual is supposed to tell about Fireworm Island, but it actually says "Changewing".
- This is the first time Stormfly uses a form of lighting by using her fire.