At the Academy, Hiccup announces to the Riders that their training mission was established by Astrid herself. The Riders express their reluctance to do her training as they've recalled their painful experiences of Astrid's brutal training missions prior. But her today's training lesson involves the Riders traveling on Dragon Island on one side and travel to the other at night, without their dragons and any camping gear, to improve their stealth skills and wild dragon defense. Though Hiccup justifies it to be very useful, the Riders still express their reluctance.
At night, they arrive at Dragon Island, Hiccup assigns Tuffnut to keep an eye of the dragons inside a cave on Dragon Island to prevent them from helping out their drill despite Fishlegs' dismay. As the Riders, except for Tuffnut, say their goodbyes to their dragons, they travel through the other side individually while Fishlegs bickers.
At the cave, Tuffnut tries to entertain the dragons with his ghost stories while keeping an eye on them, especially Toothless, as he tries to check on his Rider. Tuffnut tells Toothless that he cannot leave, Toothless, annoyed by him, wacks him with his tail and Tuffnut crashes and is stuck on a stalactite, Toothless then helps him out by shooting plasma, and Tuffnut falls down.
Meanwhile, Astrid is doing well on traveling through as she is able to protect herself against a Nadder. Snotlout, after falling down a log, he climbs back up and stumbles upon Terrible Terrors, though Snotlout feels confident, the Terrors attack all at once and Snotlout falls back down. Ruffnut encounters a Monstrous Nightmare, she cannot recall correctly about the dragon's characteristics, and she flees in fear, though somehow unable to avoid the dragon as she 'keeps coming back around'. Fishlegs is having a hard time with himself, but he becomes frightened when he travels through, unaware he disturbed a Typhoomerang behind him.
Meanwhile, just like Astrid, Hiccup is doing well traveling as he uses his dragon knowledge to easily distract two Gronckles away from him. Suddenly, he notices someone camping as he notices a bonfire in the forest, Hiccup suspects that one of his Riders is cheating and he goes to check it out.
At the cave, Tuffnut is having a hard time entertaining the dragons with his stories. While Tuffnut is busy, Toothless hears what seems to be trouble again outside and attempts to sneak past outside without Tuffnut noticing. But when he nears the exit, Tuffnut spots him and Toothless is forced to turn back. Tuffnut then chants to the dragons, that he is determined to keep the dragons prevented from exiting even if he gets annihilated by them, but suddenly they are all asleep, and Tuffnut also rests himself.
Hiccup arrives at the camp site, and calls for Snotlout whom he suspects is responsible for setting up his own camp. Suddenly someone jumps on him, and is shocked to see it's actually Dagur. Dagur cries out Hiccup in joy to see him again, as Dagur still claims that Hiccup saved him from their pretend dragon attack on Berk, especially witnessing him fighting off a Night Fury. Dagur then claims the reason why Hiccup is in Dragon Island, he claims that Hiccup is hunting dragons like Dagur also.
Hiccup pretends to accept what Dagur claims. Dagur asks whatever happened to the Night Fury he encountered, Hiccup explains that it escaped and is still on the loose. Dagur is joyful to have heard that, as he forms a new plan by hunting down Toothless and kill him, along with Hiccup.
Moments later, Dagur then talks with Hiccup, as he can't stop thinking about his encounter with the Night Fury, as he suspects that Hiccup knew every move of what the dragon would do, that prompted him to know more about the dragons' characteristics that landed him to hunt dragons on Dragon Island. One by one, Dagur observed and killed any dragon he encountered and displayed their remains in his camp.
Dagur notices that Hiccup's weapon of choice is only a 'shield', and comments to be ornate. Hiccup asks how long has Dagur been on the island, Dagur can't tell exactly, he claims to have been here for weeks now and is beginning to show more signs of paranoia, Hiccup is creeped out. Dagur then decides to pack up his gear and begins his hunt for the Night Fury along with Hiccup, whom he now dubs to be his 'brother'.
As they explore through, they are almost spotted by a Monstrous Nightmare. When it flies away, Dagur decides to kill it just for fun. Hiccup pushes his crossbow away, and justifies it by creating a false trivia that the Night Fury may have smelled their scent and acknowledge their position as they can 'smell danger' as well. Dagur is convinced and is overjoyed to see that they can form a team, and presses on.
At the cave, Tuffnut and the other dragons are pass asleep. Suddenly, the Monstrous Nightmare saw earlier by Hiccup and Dagur, rampage pass them. The dragons see it as a threat and they exit the cave to check on their Riders, while Tuffnut is still asleep and does not notice it. Shortly after though, Tuffnut wakes up and is shocked to see they have fled, so he sets out to find them.
As Dagur and Hiccup continue to explore through, one by one they meet the Riders, they are joined by Snotlout and later Fishlegs. Dagur questions Hiccup's statement of 'being alone', however, he still continues to hunt for the Night Fury. Hiccup tells them to play along to not form any suspicion towards Dagur about their dragons.
Meanwhile, Tuffnut finds Zippleback tracks and thinks that he has found Barf and Belch, but actually disturbs a wild Zippleback. He runs for his life and barely manages to evade the dragon. Meanwhile, Toothless leads the dragons of searching for their Riders.
Dagur then talks about Hiccup about them having many similarities, such as both of them being born leaders of their tribes. But Dagur then adds, that their fathers have to be eliminated to claim power over their tribes. Hiccup denies that Stoick hasn't been eliminated from anything, but Dagur tells him he can be eliminated easily, by 'saying the word' and he furiously shoots his crossbow, hinting the possibilities that Oswald was assassinated or murdered by his own son.
Just then, something rustles in the bushes and they hold their position. While doing that, Astrid stealthily sneaks and meets up with them, he tells Snotlout to keep quiet but blew her cover anyway, and she stealthily falls back. Dagur and Hiccup are expecting that it's gonna be one of the Riders again behind the rustling bushes, but to their surprise, it's actually Toothless. Dagur finally spots the Night Fury in joy, and thanks Hiccup for leading him right to the dragon.
Dagur has Toothless in his crossbow's sights, but Hiccup stalls him by saying he'd like to do the honor, resulting them to argue. But not enough as Dagur quickly continues to shoot Toothless, luckily, a group of Terrible Terrors distract him, and unintentionally fires, missing Toothless. While blinded by the Terrors, Hiccup signals Toothless to flee.
Astrid arrives saying the Terrors was suppose to be her's, but Dagur tells her that they're doing something more important than Terrors, by killing the Night Fury. While retrieving his arrow, Hiccup tells Astrid, Snotlout and Fishlegs, to turn back, find Ruff and Tuff and their dragons also, leaving Hiccup by himself with Dagur. Dagur grabs Hiccup to hurriedly hunt down the Night Fury, while Hiccup gives a false order to them to return to Berk.
Snotlout complains that they cannot find their dragons easily, he is proven wrong, when the dragons actually found them. Meanwhile, Toothless tries his best to avoid Dagur and Hiccup, Dagur is confused why isn't it attacking. Hiccup gives him a theory that it's only luring them to a trap and recommends that they turn back, but Dagur is relentless and continues to hunt him down.
Meanwhile, Tuffnut finds Barf and Belch resting, and sneaks up on them to teach them a lesson after ditching him back to the cave. Suddenly, Ruffnut kicks him and asks what brings him outside. Tuffnut tells Ruffnut that he was planning to check on her, she then asks why is their dragon outside. Tuffnut responds that they were hungry for some 'outdoor food', but confesses that the dragons ditched him. They then argue at each other loudly, they then decide to regrouped with the others, but finds that they're already near them, due to their loud voices Astrid and the others manage to find their location but tells them to argue silently.
Toothless is chased relentlessly, Hiccup and Dagur pauses a bit, as Dagur suddenly fires an arrow with flames towards the sky. Hiccup wonders what was that for, Dagur confesses that arrow he shot was actually a signal to the thousands of Beserkers waiting for Dagur's orders just out in sea, and they respond back with Dagur's rendezvous signal with hundreds of flamed arrows at their location, Hiccup then becomes worried that Dagur and his men will be able to capture Toothless, as Toothless is no match for the Beserker Armada.
Dagur plans to drive out the Night Fury towards the Beserkers' field of vision, Hiccup comments it's not very fair or sporty, but Dagur doesn't care as he only wants the dragon killed and wear his skull as a hat. Toothless has run out of land to flee, and finds himself trap in Dagur's sights as he is stuck in a cliff and is a sitting duck. Unable to stand and watch Toothless suffer any longer, Hiccup has no choice but to expose himself the truth that he and the others on Berk ride dragons, by calling Toothless to him and Dagur witnessing it.
Dagur was right all along but is angered by he and Stoick lying to him, Hiccup explains that his father was only trying to maintain the peace with their tribes. But Dagur feels that he was fooled, and declares to Hiccup that he is no longer his 'brother' but his 'enemy'. Hiccup accepts his decision but warns him that they will attack with their dragons, and they attempt to leave.
However, Dagur throws three bolas at Toothless and is pinned down. Dagur charges for the kill, but Hiccup blocks him with his shield. Dagur throws daggers and other weapons at Hiccup and is pinned, but Toothless helps him out by wacking Dagur with it's tail, but gets him closer to his crossbow, which Hiccup's shield hit earlier.
In the ensuing fight, Dagur keeps Hiccup at bay while also hitting Toothless with some arrows. Hiccup fights back by revealing to Dagur his specialized shield, by transforming it to a crossbow. Dagur dodges Hiccup's attack and mocks him but still dubbing him as his 'brother', Hiccup responds that he is not his brother and shoots a bolas at a branch, whom Dagur thinks he miss. Hiccup pulls the rope causing the branch to plummet down Dagur.
Hiccup makes a break for it, by cutting the ropes on Toothless, but Dagur quickly regains his strength and tackles him. Hiccup is being crushed by Dagur, but Toothless manages to take off the weakened bolas at his head and shoots a plasma blast at Dagur. Hiccup finally releases Toothless and he finally fends off Dagur, proving no match against Toothless.
Dagur retreats but signals the Beserkers a dragon attack. Hiccup orders the Riders to return back, but Snotlout recommends that they can take on the Beserkers. But Hiccup tells them not tonight, as they are unprepared but is certain Dagur will be back and when he does they'll be ready.
Moments later, the Beserkers were unable to capture the Riders. But Dagur informs them what happened, a Beserker soldier brags that he'd kill Hiccup for hiding the truth, but Dagur angrily tells him no one shall hurt Hiccup, except for himself and also capturing his primary dragon, the Night Fury, thus discarding the former alliance on Berk.
Hiccup and the Riders flee the scene on Dragon Island and head home for Berk, fully aware and concerned that a another great threat has emerged.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Christopher Mintz-Plasse as Fishlegs Ingerman
- T.J. Miller as Tuffnut
- Brook Chalmers as Berserker Herald
- David Faustino as Dagur the Deranged
- Zack Pearlman as Snotlout
- Julie Marcus as Ruffnut
- This is the third episode in a row that there has been no narration.
- Hiccup's new shield reveals that it can transform into a Crossbow.
- Both Stoick (second time) and Gobber don't appear in the episode.
- Astrid is shown to be creating training missions.
- While Dragon Hunting with everyone, Dagur mentions that the Berserkers former chief (and father) Oswald the Agreeable was "eliminated" when he compares himself to Hiccup, further arousing the suspicion that Oswald was murdered by Dagur.
- When Hiccup talks with Dagur there's a moment when Hiccup's shield disappears for a few seconds.
- While sitting on Toothless, Hiccup's right leg is completely gone and we can see only his boot.
- When the teens are leaving Dragon Island Hiccup doesn't have his shield.
- In this episode we can see that Stormfly sleeps while she is standing.
- For some reason, Barf & Belch were not with the other dragons when they found their riders.
- Dagur says that he fought a Deadly Nadder while he was on the island, and that he got shot in the leg with one of it's quills. But a Nadder's quills have been said to be poisonous.