"As you fly through life it's always good to know who you can trust... and who you can't. I know I can always count on Toothless. And it's important for him to know... that no matter what... he can count on me." - Hiccup
The episode starts with Hiccup, Astrid, Fishlegs, Snotlout, Ruffnut, and Tuffnut flying on their Dragons over the opposite side of the island. Hiccup teaches how trust is important with your Dragon and demonstrates this by jumping off of Toothless and having him catch him. Congratulating him on the catch (though saying it was quite close) he offers one of them an opportunity to try. Snotlout attempts this, however Hookfang decides not to catch him until he was too close to the ground; close enough to crash into Mildew's house on the cliff.
At home, Stoick, madder than usual, had to deal with Mildew's complaints twice already. He explained to Hiccup the Dragons' acts reflect on him which reflects on Stoick, and he told him to fix Mildew's roof the next morning for tonight was "boot night", a time where the whole village lets their boots air out over night.
During the night, a mysterious figure (only distinguishable with large claws) swipes away the boots, however leaving footprints in the snow.
As it turns morning, Stoick sets out to grab his boots to discover they're gone; they're all gone. Fishlegs, noticing the footprints, report the shape resembles that of a Hideous Zippleback. Mildew arrives proving this theory by showing them Barf and Belch were asleep beside a pile of boots in the Dragon ring, some torn. To Mildew's dismay, Stoick only orders they be more careful.
Atop one pillar, the teens discuss how to keep the dragons under watch over the night (Fishlegs disliking the idea of going out at night) and temporarily formulate the Dragon United Monitoring Brigade or "DUMB" (wearing sashes that indicate so). They put this plan of action to work, and Astrid comes knocking on a random Viking's door to state her duty and he (she) should report if there is any troubles with the Dragons. However, she is considered of annoyance and is rejected. Meanwhile, Snotlout, without his Dragon, is on lookout when he spots Gobber, getting upset Gobber isn't respecting his "position of authority". An uneasy Fishlegs in on lookout as well when Ruffnut and Tuffnut, trying to scare him, approach in the form of a dark ominous shadow. However, this isn't what scared Fishlegs: it was Hookfang wandering around behind them (though the twins still argued about who really scared him). Hiccup, flying on Toothless, doesn't notice Hookfang's peculiar whereabouts and conclude all the dragons are peacefully sleeping.
Though still, a figure again creeps into the Great Hall and scratches, rips, and destroys some of the objects in it. This time the claw resembles a different Dragon species than the boot stealing one, seemingly another Dragon.
In the morning, the Vikings, noticing the defacement of the Great Hall's furnishing, complain about a Monstrous Nightmare being responsible for this (as yet again appointed by Fishlegs' deductions). Snotlout admits he remembers Hookfang running amok for hours the previous night during their watch. Again, Mildew wanders in, hoping for a punishment for the dragons, and is once again disappointed about the level of penalizing: keeping the Dragons under lock and key. However, Hiccup still doubts the Dragons would be doing this and if these are a Dragon's actions at all.
Hiccup, Astrid, Fishlegs, Snotlout, Ruffnut and Tuffnut hold a conversation in the Dragon Academy about this matter. They comment on how they choose not to admit their Dragons could have done this damage. Hiccup makes a point on how the footprints found during the night when the boots were stolen aren't as deep as an actual Zippleback's, and how a Monstrous Nightmare, supposedly on a rampage, would probably scorch objects around him/her as well. When he brings this up to his dad, he demands full proof it was something other than a Dragon.
That night, Toothless investigates a noise that was heard in the armory. A Viking, a few houses nearby watches him as he enters. Toothless discovers the noise came from a fire that spread to a cylinder containing explosive fluids, resulting in the destruction of the armory as well as all the weapons within it. As Toothless escapes the witnesses think Toothless created the explosion and point this out as they tried to extinguish the flames. Hiccup is in total disbelief, and Stoick orders the Dragons to be sent off to Dragon Island. Mildew celebrates and tells Hiccup to fix his roof after the Dragons are dropped off.
Morning eases in and the teens drop off their Dragons. They say their goodbyes, but Hiccup promises he'll be back for Toothless when he gets this whole matter cleaned up. When they leave on the ship, Hiccup makes an accusation Mildew was responsible for all of this, supporting it by saying Mildew, living on the other side of the island, was mysteriously consisting of the knowledge of Toothless' whereabouts during the armory's explosion.
As Hiccup fixes Mildew's roof, he drops down into the house to find clues to convict him of this crime. He succeeds by finding a pair of dragon feet, able to be worn as boots, and a Dragon claw at the end of a stick. Before he takes the evidence, Mildew walks in with his sheep and, after some of his suspicions get disproved, walks away with the claw and boots, unknowing Hiccup dangles from a rope above him. Unfortunately, he's almost caught when a bead of sweat drips onto Fungus. Hiccup hoists himself atop his house to see what Mildew is up to and finds him disposing of his Dragon-like recreations into the ocean.
- 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
- Tom Wilson as Bucket
- Tim Conway as Mulch