One year passed since Hiccup defeated the Red Death. Vikings and dragons now co-exist on the island of Berk. Hiccup and the riders have a best trick competition for their dragons, Hiccup usually being the best. Afterwards, Hiccup heads back to the island and sees Berk seemingly 'under attack' by the dragons' natural behavior and the Vikings have a hard time continuing their daily lives. Although most are willing to co-exist with the dragons (despite their behavior), there are those who will never accept them, as Hiccup states, and they will do anything to drive the dragons off of Berk for good.
Later at night, an old grumpy Viking named Mildew is awakened when his house rattles and shakes violently. As he goes outside, he discovers a dragon made the disturbance by sitting atop of his house, but that's not the worst part. He discovers that a herd of Gronckles has devoured his entire cabbage field. Mildew grows angry that the dragons have gone too far and travels through the main part of Berk.
The next morning, Stoick organizes Berk's food supplies, but Mildew interrupts as mentioned by Gobber, with his 'complaint of the day'. Mildew complains the dragons interfered on Berk's Viking lifestyle, his chants are overheard by the entire village, and the Vikings listen to Mildew's statements, supporting him. Mildew points to a solution that the dragons should be caged before any damage can be done, the crowd supports his suggestions. Hiccup overhears the conversation and tries to justifies the dragons behavior, but Stoick confidently takes Mildew's problem promising to fix it. Mildew warns him and speaks for everybody that he must do it quickly. The crowd congregates and chants at Stoick.
At Stoick's house, Stoick says the dragon problem hasn't been fully appropriate or resulted in good use and reconsider letting dragons roam freely through Berk, but Hiccup suggests he deals with the problem by himself. Stoick agrees and lets him do it starting tomorrow.
The next day, Hiccup and Toothless begins their attempt of controlling the dragons when they spot a wild Nadder that tries to grab a lady's bread. Hiccup goes in and tries to discipline the dragon. Things go well for a brief moment, when a Gronckle suddenly interrupts and startles the Nadder, causing more trouble. Everything goes from bad to worse when Hiccup spots a dragon fight, causing the sheep to run and scatter. One sheep catches on fire and Hiccup goes after it while Toothless tries to stop the fight. Hiccup runs further into the plaza and sees he isn't the only one having a hard time as the villagers are being overrun by the dragons' unpleasant behavior. Hiccup is unable to catch the sheep and drops the bucket filled with water. The other riders watch overhead and observe his doings. Hiccup finally stops the sheep that's on fire. However, it's 3 o'clock and it's the time where the dragons "relieve themselves". Unable to hide from the poop shower in time, Hiccup gets hit directly in the face.
Hours later, Hiccup fails to control the feud and every part of his body is in pain (including his prosthetic leg). Astrid greets him and asks how his day was. Hiccup responds his day as one of the worst. Stoick arrives to inform Hiccup that the entire plaza looks like a war-zone and Hiccup states it's just Phase One of his 'master plan' and it's fully complex (but not fully prepared yet). Stoick is glad to hear it and makes sure Hiccup's plan goes into motion because Mildew stirred up the villagers to get rid of dragons and if he is unable to fix it soon, the villagers 'will be calling for their heads'. Hiccup ensures Toothless that his head isn't going anywhere. Astrid states there are like a 'bazillion dragons' and there's only one of him and asks Hiccup if he does have a master plan.
The next morning, Hiccup's actual plan is to train dragons inside the abandoned arena to where they use to kill them. The dragons are a little nervous, and Fishlegs explains because they're sensitive, especially Meatlug because she lost a cousin there. Hiccup reveals to Astrid he didn't inform and ask permission to his father to use the arena as a training site and goes behind his back and not talk about it. Hiccup explains to everyone the dragons can't co-exist properly in human civilization and can't live properly without their help and asks everyone to join him control their behavior. The twins got it wrong and state to help dragons blow things up and to do that is to make them really really mad which is not a problem because they irritate everybody. Hiccup gets serious and tells everyone Mildew wants their dragons caged, which isn't a good thing. The twins feel bad, but Tuffnut points to Ruffnut and says she's sorry. The next problem is the dragons eat everything in sight and to resolve this, he demonstrates it to everyone by Toothless being the example. He explains when a dragon grabs something it's not suppose to have, it can let go if you give it a little scratch under the chin. Snotlout interrupts and tells Hiccup he has a better one; he throws the food to Hookfang, and to make him drop it, he gets in his face and yells harshly for him to drop the food. Hookfang gets annoyed and drops it, but bites his rider instead. Hiccup tells everyone to get ready and is about to put the plan in motion together, while they wait for Hookfang to let go of Snotlout.
They head into the plaza but find it suspiciously empty and quiet. It seems the problem is done, but a huge explosion occurs and the riders head to it. The dragons (including the riders') raided the town's food storage and ate everything. Mildew arrives and states Stoick warned him, but didn't listen and made it worse by "putting a bunch of teenagers in charge" and tells Stoick one last time to cage the dragons for their own good. Hiccup tries to convince his father he can fix it, but Stoick had enough and distrusts their plans of controlling dragons after seeing their own dragons can't even be controlled. Stoick orders Bucket and Mulch to man the boats and catch more fish, but Mulch states it's too late because it took them 6 months to catch all those fish with the freeze coming soon. Stoick tells them to at least try. Mulch apologizes and blames Bucket to not tell the chief it's too late.
Hiccup's pleas for another chance to fix the situation is ignored, as Stoick is too busy refilling Berk's food supply as soon as possible and orders Hiccup to cage the dragons, but Mildew changes it by sending them away permanently so no more damage can occur in the island. Stoick has no choice but to go with Mildew's plan, and orders Hiccup to cage the dragons in the night and at dawn he'll send them away.
Near nightfall, at the Great Hall, the riders are upset that their dragons are going to be caged and sent away. They recall their good moments with them and they get to the caging. Hiccup is still relucant and is desperate to not let it happen because Toothless is the best friend he ever had. Mildew says his last goodbyes to Toothless happily and explains to Hiccup his mistake was thinking dragons could be trained. He added that dragons are going to do what dragons are going to do because it's their nature and nature always wins. Hiccup comes up with an idea after hearing that because it's absolutely right. He heads to the arena where the riders are about to cage their dragons after saying their goodbyes and apologies. Hiccup barges in and flips the switch that locks the cage and explains to everyone they're not locking their dragons. Astrid asks if Hiccup changed Stoick's mind or is he going behind his back again. Hiccup responds it's one of them and tells them his plan that dragons are going to do what their going to do because its their nature, and they just need to learn how to use it.
The next day, Bucket and Mulch have no progress in their nets. Hiccup tells Snotlout to let Hookfang dive into the water and scare the fish through the nets. Bucket and Mulch quickly grab the overfilled nets and happily thank them. Next stop, the riders head for Mildew's field and help him plant cabbages and 'fertilize' it with the help of the dragons poop that acts as fertilizers for the crops, saving Mildew three months of work. Next, Barf and Belch scare a group of boars and Hiccup and Toothless redirect them toward an inn and locks them up for Berk's food supplies. The riders are astonished of what happened and ask how Hiccup knew it was going to work, again he explains they're dragons and they need to learn how to use their behavior together, and not work against it. They should thank Mildew but he is seen with Stoick that the dragons are not caged yet and is not happy for what the dragons did to his field. Stoick is seemingly mad that this is not what he asked for and gathers the riders to the arena. Gobber and Stoick slowly arrive and is about to tell something to the riders responsible. The riders all think that they're going to be sent to jail and Hiccup tries to convince his father he should be the only one punished not the others. But Stoick states that they all were in it and they all disobeyed his orders, Mildew watches on and is excited for Stoick's punishment. Stoick seems to be mad after they went behind his back after letting the dragons help Berk and taking the arena without permission and in turn which Stoick wants to tell them by himself, Gobber interrupts that they are getting their own Dragon Training Academy. Gobber also tells them that Stoick is so proud of them especially Hiccup.
Stoick grants them access to the arena and releases their dragons. Mildew walks away in anger. Hiccup ensures Stoick that it's not gonna be a problem training them with Toothless and the riders are with him together. Hiccup celebrates by drawing the riders and their dragons together as a rememberance and the riders enjoy their dragons once again with their daily lives and helps around at Berk such as gathering food supplies. They open their academy and name it The Berk Dragon Academy and Hiccup gives the closing narration to the scene.
- 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 and T.J. Miller as Ruffnut and Tuffnut Thorston
- Zack Pearlman as Snotlout Jorgenson
- Tim Conway as Bucket
- Tom Wilson as Mulch
- Stephen Root as Mildew
- This episode introduces the recurring villain, Mildew, a grumpy complaining Berk Viking farmer who used to be a dragon killer but because of the peace with the dragons, he no longer can do that. Now he has made it his life task to attempt to evict or kill the dragons on Berk.
- The fact that the other villagers built Mildew's house outside the village implies the others don't like him a lot. Also the way Gobber says, "Ah. Here's Mildew with the complaint of the day!" to Stoick implies that even kind and friendly Gobber doesn't like Mildew.
- This is the first time Hookfang's habit of being disobedient to his rider, Snotlout, is shown. Later on in the series, it's a running gag that Hookfang is disobedient towards Snotlout, or is distracted by little things around him and not paying attention to Snotlout.
- The old Dragon Killing Arena is converted into the Berk Dragon Training Academy.
- This episode's lesson in the Berk Dragon Academy: How do you get a dragon to drop something it's not supposed to have.
- The roles of the dragon rider teens in the Berk Dragon Academy are as follows:
- Hiccup is the main dragon teacher and the head of the Berk Dragon Academy. While his specialty is Strike Class dragons specialist, he is also very capable of handling the other dragon species.
- Astrid acts as Hiccup's right hand woman (and probably also his enforcer if it's going to be needed). Besides being Hiccup's right hand woman, she is also the Sharp Class dragons specialist of Berk Dragon Academy.
- Fishlegs is the logmaster of the Book of Dragons. He is also the Boulder Class dragons specialist of the Berk Dragon Academy.
- Snotlout is the closest one in Berk Dragon Academy to being a Stoker Class dragons specialist.
- Ruffnut and Tuffnut are the specialists of the Fear Class dragons of the Berk Dragon Academy.