- "A deadly flower, a venomous sea Dragon, and Mildew's butt: three things I never really thought I'd have to deal with in the same day. But I'll do anything for my Dragon."
- The Scauldron makes its first appearance.
- Trader Johann is introduced.
- Stoick reveals to have named his dragon Thornado.
"Berk is a small island in the middle of nowhere. So when we get a taste of something new, we tend to go a little overboard. Unfortunately, 'new' isn't always good.
Berk's favorite trader, Trader Johann, arrives on Berk just as dozens of excited villagers rush down the harbor to greet him and his new deliveries of fine goods. Hiccup arrives also to get new ink as he ran out a while ago, unable to finish his drawing of Toothless. Johann tells him the ink is exotic as it came from a colossal squid that he claimed to have wrestled with in the Northern Waters and requires a great exchange, Hiccup at first offers a Spyglass in trade, but when Johann says he has already and yet only two eyes, he offers him a wench for the ink instead and Johann accepts.
Stoick informs his son, he'll be going to his yearly meeting with the Chief of the Shivering Shores and will return in a few days. As Stoick begins to leave, he reveals his dragon's name: Thornado, and they set off. Meanwhile, Mildew arrives and asks Johann the goods he came for, which Johann replies is all prepared and he is in return, paid with Mildew's cabbages, Mildew request Johann to take it to his house.
Just then, a Terrible Terror sniffs Mildew's goods, Johann tells the dragon to stay off limits, but it refuses, so Johann rudely drags it away. Toothless sees it as a threat and aggressively confronts Johann causing him to smash Hiccup's jar of ink, Hiccup calms him down and apologizes. Hiccup is upset as he is informed by Johann that was his last jar of ink. At the Academy, Tuffnut brings in a statue they got from Johann, Hiccup thinks the Twins bought it for decoration, but the Twins are actually using it for target practicing. Every dragon takes a shot of shooting the statue, but when Toothless tries his turn, he sneezes and misses. His sneezing escalates, bursting runaway plasma blasts. Hiccup becomes concern for Toothless's strange condition.
Moments later, Hiccup and Astrid fly through Berk, but Toothless struggles as he starts sneezing again, he soon flies out of control and eventually crashes. Hiccup wonders if he has a cold, Astrid then notices the Terrible Terror prior having the same condition as Toothless. At their home, Gobber tries to give him something for Toothless to be cured but Toothless ruins it with it's sneeze, just then Astrid arrives informing Hiccup of an emergency. Outside, they notice the other Riders' dragons becoming suddenly ill as well, and they fly out of control. Hiccup realizes the mysterious sickness is infecting the other dragons as well, Gobber proposes to meet the Village Elder, Gothi for help.
As Gothi inspects Toothless's health, she discovers the situation. As she draws her scriptures, in which Gobber translates, saying their dragons are allergic to something 'new' on the island, Astrid tells them there's a lot of new things that were brought in to the island due to Trader Johann, Gothi then tells them in her scriptures, saying unless they dispose all of the new things in the island their dragons' illness will continue to worsen.
As a result, the Riders inform the villagers of Berk to dispose all their new possessions they bought down in a pit for the sake of the dragons, some are reluctant to let go, such as Fishlegs who refuses but eventually throws his botany book thanks to Ruffnut, and Gobber's silk underwear who Gobber denies he bought it, but eventually admits and throws it away.
The next day, the Riders discover their dragons still severely ill and unsuccessfully tries to make them feel better. The Riders are confused, Hiccup suspects that there is still someone who refuses to give up their item from Johann. Just then. Stoick arrives from his yearly visit at the Shivering Shores, he quickly discovers the situation about the dragons being sick. Hours later, Stoick and Hiccup concludes that there's still something in the island that's making their sickness worse, just then, they hear Thornado in distress. When they go outside, Stoick discovers his dragon is now infected by the mysterious epidemic as well. Quickly, they retrace Stoick's steps by looking around the area of where they landed, that caused Thornado to get infected.
Hiccup tells them to find anything unusual in the area, Fishlegs spots the Twins the first thing he sees unusual, headbutting near them. But Hiccup then notices strange flowers planted near them too, Fishlegs identifies the flower to be a Blue Oleander thanks to his botany book, Hiccup asks for it's characteristics, Fishlegs recalls that these flowers bring poison to reptiles, meaning also poisonous to their dragons. Hiccup quickly request Fishlegs to find and dig for his book back in the pit to find a cure. Meanwhile, Astrid asks how did the flowers even got to Berk, the Twins answers by saying that Mildew planted them one day.
Stoick suggests they pay a visit to Mildew, when they arrive at his home, Mildew denies that he intentionally planted the flowers he bought from Johann, to bring mayhem for the dragons as he claims he intended to plant the flowers as decorations for the Town Square. Despite Hiccup and Astrid accusing him, Stoick reluctantly tells them to just leave. Hours later at the square, Fishlegs arrive with his botany book, but heavily breathing, he tells that he recalled a dragon who feeds on the blue oleander, concluding it to be immune to it's poison, called the Scauldron. Fishlegs claims that it's venom can reverse the blue oleander's poisonous effects thus curing the dragons if they only lived in a perfect world, as Fishlegs is informed by the Book that the dragon claims to have no venom. But Gobber tells the Book to be wrong, as he recalls his confrontation with the Scauldron, describing it to be a colossal and fierce creature that can burst boiling hot water to it's victims, and is certain the dragon does have venom.
Hiccup assembles Gobber and Stoick to go find a Scauldron, as the others stay to take care of their ill dragons. Before embarking on their hunt, Hiccup comforts his dragon, especially Stoick also with Thornado, who he now sees himself to be a change man than before. As they set sail, Stoick also brings along Mildew, who protests that he has done his job of digging out the plants, but Stoick tells him it was him who caused this in the first place and insists he comes along. They put their plan into motion, by luring a Scauldron with it's favorite meal, blue oleander flowers. Moments past, and no signs of a Scauldron, but finally one arrives. They must manage to put the Scauldron on deck for a chance to drain it's venom, however, the Scauldron charges to the ship and attacks viciously, tipping the ship, causing the basket of blue oleanders to descend down and the Scauldron eats it. Stoick and Gobber seizes the opportunity and manages to lasso it, but struggles to pull it on deck. Stoick orders Sven to throw a barrel in it's mouth for Hiccup to drain it's venom, however, the plan falls apart as the barrel is crushed and Sven is wacked by the dragon's tail causing Sven to fly off overboard. The Scauldron's tail sneaks up behind Hiccup, but luckily Stoick pushes him aside and rescues him, but gets brutally wacked and thrown back and forth, but Stoick still manages to grab on to the tail and finally pins it down.
Hiccup assists Gobber in pulling the Scauldron's mouth in between the mask of the boat. With everyone's hands full, it's up to Mildew to get the venom by grabbing the bucket and fill it up in which Stoick angrily orders him to do it. However, Mildew waits too long as the Scauldron begins to burst boiling hot water at them, forcing Hiccup and Gobber to let go and get to cover. Unable to hold the weight, the pole of the ship snaps and Stoick falls into the ocean. The ropes holding the Scauldron snaps also, and the Scauldron is freed. Mildew watches as the Scauldron spots him and he runs for his life, however, the Scauldron notices a blue oleander sticking in his butt and the dragon bites it, painfully injecting venom on Mildew. After that, the Scauldron returns to the ocean, while Mildew screams in pain requesting to get the poison out of him.
Hours later, Mildew must undergo painful extraction of the venom out of his buttocks in Gobber's smith, where Gobber performs the extraction. Just outside, the Riders watch and listen to the screams and pains Mildew is having as the poison is being extracted. As the procedure is finish, Gobber tells Hiccup that extracting the poison out of Mildew's butt was the most disturbing things he has seen in his life so far, and gives Hiccup the cure as he sets out to the forest and scream there. Moments later, the antidote is given to the dragons, Stoick and Hiccup waits for the cure to take effect, and then finally, the dragons are all better now.
The next day, Hiccup finally finishes his drawing of Toothless in the book. As Hiccup watches outside the window, noticing the Riders' with their dragons flying in the sky in joy, as the epidemic is finally gone.
- The Scauldron is introduced.
- It is revealed that the Scauldron is venomous.
- Trader Johann is introduced.
- It is possible that a Pricklepine or at least the egg of a Greater Pricklepine appears on Trader Johann's boat. It appears to be in a sack. Later, the sack is thrown in with the rest of the goods purchased from Trader Johann.
- According to Tuffnut, the twins traded their great-grandfather's skull for a statue.
- They got to keep his clavicle.
- It is rumored that Gothi can tell when you can die by looking at your tongue.
- When Gobber says he is going into the forest to scream, he actually does.
- Hiccup uses the feather he got in the previous episode.
- 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
- Julie Marcus as Ruffnut Thorston
- T.J. Miller as Tuffnut Thorston
- Zack Pearlman as Snotlout Jorgenson
- Stephen Root as Mildew
- Michael Goldstrom as Trader Johann
- Thomas F. Wilson as Bucket