这一集以回顾上一集发生的事情开始， "In Dragons We Trust", and the current situation on Berk, with the armory being destroyed, and the dragons having been banished from the island, with Hiccup suspecting Mildew is responsible. The recap ends, and the scene shifts to the present day, to the dragons on Dragon Island. Hookfang and Barf and Belch fight each other, but Toothless quickly intervenes before any blows are exchanged. He goes to a slightly sheltered spot beneath a rock, where his saddle is, and looks at it sadly, before gazing out over the ocean in the direction of Berk, missing Hiccup.
The scene changes to Hiccup on the shores of Berk, who also gazes out over the sea. It's revealed after his discovery Mildew framed their dragons, he and the other teens search for the evidence he threw over the cliff-side, hoping to find it washed up on the beach. Snotlout loudly complains they've been out searching for hours, but Hiccup tells him they've only been searching for ten minutes, and all Snotlout did was build a tiny structure of sticks. He inquires what it is, and Snotlout tells him the pitiful construction was 'Snotlout Manor'. He states all he needs is a queen, trying to flirt with Astrid, but is quickly rejected. He's interrupted as Tuffnut stomps on the structure, stating he's 'Storming the Castle'. Fishlegs tells Hiccup their chances of finding the things Mildew threw over the cliff are slim, comparing it to the chances of Snotlout and Astrid dating. Astrid goes over to Hiccup and tells him they may never find any evidence. Just after she tells him this, Snotlout calls out in excitement, and Hiccup rushes over to see what he found, but to his dismay, Snotlout only discovered an old club that he lost when he was little.
The scene shifts to the forge, where Gobber crafts weapons to restock the destroyed armory. Stoick is present and tells him he needs to work as quickly as possible, because, without weapons, Berk is completely defenseless. Although Gobber states he shouldn't have sent the dragons away, Stoick tells him he had no other choice. Gobber describes the terrible situation that could befall the island if they were attacked, especially by their most fearsome enemy: Alvin the Treacherous, who would kill everyone in order to claim Berk.
The scene changes and Alvin the Treacherous is revealed to be a large, intimidating warrior who lives on an island with a group of Vikings known as the Outcasts, all of whom were banished from Berk as punishment for committing terrible crimes. Much like Berk, Outcast Island is inhabited by wild dragons, but instead of taming them, Outcasts still fight them. Dragons viciously attack the Outcasts, destroying all present structures and vegetation with fire. Alvin flips over a catapult and shoots down a Monstrous Nightmare. He enters the Outcasts' version of the Great Hall, which is located inside of a dormant volcano and is sealed with a reinforced door. He speaks with his Lieutenant, Savage, and devises a plan to sail to Berk, and dock there under the cover of night. Savage inquires why they aren't bringing the entire army. Alvin states they're not sailing to Berk to fight Stoick. Instead, they're going there to find one man: the "Dragon Conqueror", referring to Hiccup, but unaware of the Conqueror's true name or identity. Thinking Hiccup is a master at fighting dragons, Savage tells him he heard stories about the Dragon Conqueror, such as him being ten feet tall, with the strength of a dozen men. Alvin states he shouldn't be too hard to handle, confident he's capable of overpowering the Conqueror.
Back on Berk, Hiccup tells his father Mildew is responsible for the destruction of the armory. Stoick explains, that while he believes his son, Hiccup must have evidence in order to accuse a man of high treason. Later, as the sun sets, Hiccup and Astrid walk together on the cliffs. Hiccup states they need to prove Mildew framed the dragons, as it's the only way to get them back. Astrid looks over the cliff and sees a ship in the distance, anchoring in an unusual location. She asks why one of their ships would dock there. Hiccup takes out his spyglass and looks through it to see the ship more clearly. He tells her it isn't one of their ships, and they need to tell his dad quickly. They run toward the Great Hall.
Later that night, Alvin and his men dock on the beach, and they go in search of the Dragon Conqueror. In the Great Hall, many people are worried. Stoick attempts to calm them down, as panic is what the Outcasts will be relying on. A Viking named Sven comes in and states there are 30 Outcasts coming, and all of them are armed to the teeth. Gobber points out with no weapons, they're defenseless. Mildew spitefully chooses this time to attempt to pass the blame onto Hiccup. Stoick ignores him and announces he, Gobber, and several other Vikings will go into the woods to draw out the Outcasts. He also orders Mulch and Bucket to get the children and the elderly to Thor's Beach, as there are caves there where they can hide. They all leave, but Astrid insists on staying and fighting. Stoick gives her an Outcast hatchet that originally belonged to Alvin but orders her to go with the others to protect them. She nods and leaves. Hiccup tells Stoick he needs to get the dragons so they can defend themselves. He allows it but tells him to be careful, as he has no idea what Alvin is capable of. Stoick, Gobber, and two other Vikings leave immediately after Hiccup does and go into the forest to set up an ambush.
The scene switches to a cliffside, where Fishlegs sits on the ground, composing poetry about how much he misses Meatlug. He states a verse, 'My heart is empty,' when he is interrupted by Alvin, who states, 'Nothing rhymes with 'empty'.' Alvin grabs him by the collar and demands him to tell him the Dragon Conqueror's name. Fishlegs, however, only screams at the top of his lungs, and Alvin angrily throws him off the cliff into the ocean. Hiccup runs toward the docks. When he spots a group of Outcasts approaching, he is nearly discovered and is forced to hide behind a house. He hears something behind him and turns to see Fishlegs, who tells him that Alvin is looking for him, 'The Dragon Conqueror'.
Alvin and Savage walk through the village and see the armory has been destroyed. They locate Stoick's house. Alvin kicks down the door and barges in, demanding Stoick reveal himself, but he isn't there. One of his men approaches and states he found fresh tracks leading into the forest. He also received reports of a large man with a bucket on his head (Bucket) heading down to the beach. Alvin decides they should split up. He orders four of his men to search the woods, while he and the other go to the beach. He asks Savage how many hostages he thinks a Dragon Conqueror is worth. Hiccup and Fishlegs overhear their conversation while hiding, and Fishlegs asks what they're going to do. Hiccup tells him to go to the woods and warn Stoick, while he tries to get ahead of Alvin and warn Mulch and the others.
Meanwhile, in the forest, Gobber explains when the Outcasts come looking for them, they'll ambush them. Stoick asks what weapons they have with them. Gobber tells him they have two frying pans, a rolling pin, and a kitchen knife. Stoick doesn't have high hopes for the ambush, but Gobber throws the kitchen knife at a tree, which causes it to split in half. Elsewhere, Mulch leads the people to the caves but notices Bucket has gone missing. A little girl tells him Bucket went back to get her stuffed lamb, 'Lamby'. Mulch goes back to look for him and finds him with the lamb. Bucket states he couldn't help himself, as the little girl had been crying. Mulch sighs and replies his bucket is hard, but his heart is soft. The two start to leave and return to guide the others but are caught at spear point by Alvin and his men, who state they followed Bucket. Hiccup arrives but hides when Alvin appears, and realizes he was too late to warn the others. Back in the forest, the Outcasts chase after Gobber and corner him, only to discover that it was a trap when Stoick and the others take them down. The Vikings hear someone coming, and Stoick tackles him, only to discover that it's Fishlegs, who tells him that Alvin is looking for Hiccup.
On the beach, Alvin and the Outcasts hold Mulch, Bucket, Astrid, Snotlout, Ruffnut, Tuffnut, Mildew, and the others hostage. Alvin introduces himself to those who don't know him and tells them he isn't after them, but after the Dragon Conqueror. Mildew tells Astrid to say goodbye to Hiccup, and raises his hand to get Alvin's attention, planning to tell the Outcast leader about Hiccup, and thus be rid of him. Astrid quickly elbows him in the face and knocks him out; she catches him and tells Alvin her "grandfather" is frail, and he needs his rest, after which she drops him in disgust when Alvin turns away. Alvin continues on, saying if they tell him who the Dragon Conqueror is, they can all go free. Snotlout decides to "show Alvin who's a conqueror"; he takes out his club he found on the beach and charges Alvin while his back is turned. When Alvin turns around and glares at him, Snotlout gets scared and offers the club to him instead. Alvin tells him to check his pants because he thinks he soiled himself. Alvin turns his back again, and this time Astrid throws her hatchet at him. Alvin catches it and states he's happy to have his old hatchet back. The Outcasts push Astrid to Alvin, who tells her trying to kill him wasn't very smart. He asks who the Dragon Conqueror is, painfully yanking back on her braid. Hiccup intervenes and reveals himself, telling Alvin to leave her alone. Hiccup comes before Alvin and tells him he's the Dragon Conqueror, but the Outcasts laugh at him, with Alvin calling him "Stoick's little embarrassment". Hiccup points out there are no dragons on Berk, and he's the one responsible for that; he gives Astrid a nod, and she picks up on his hint. She adds how the all the dragons are afraid of Hiccup, and he even conquered a Night Fury. Alvin accuses Hiccup of bluffing, but Hiccup states there's only one way to find out: take him to Dragon Island.
Much later, Alvin and Hiccup are gone, while everyone else remained captives of the Outcasts still left on the island. Stoick and Gobber ambush them and capture the Outcasts. Stoick attempts to interrogate one of them about Alvin's location, but Astrid tells him Hiccup gave himself up to Alvin, and they're on their way to Dragon Island. Meanwhile, at daybreak on Alvin's ship, Hiccup is revealed to have been forced to stand against the mast at spear point by Savage and another Outcast warrior. Alvin states rhetorically Hiccup surely heard stories from his father about him. Hiccup feigns ignorance and casually denies Stoick ever told him anything about Berk's most feared enemy. He intentionally irritates Alvin but tells him he'll do what he says if Alvin leaves his people in peace. On a different ship, Stoick, Gobber, Astrid, Snotlout, the twins, Fishlegs, and several other Vikings arm catapults, while Stoick tells them they'll lay down cover while Astrid and the others get the dragons. The twins volunteer to beat up Alvin, but Stoick tells them it's not about Alvin, but about Hiccup: they're there to bring him home.
The scene returns to Hiccup and Alvin, who land on Dragon Island. Hiccup is escorted from the boat by the armed band of Outcasts onto the beach. Toothless emerges from the large cavern made previously by the Red Death. The Outcasts are awestruck and fearful, wondering what it is, to which Hiccup replies, in a somewhat cheerful tone, the dragon is a Night Fury, 'The unholy offspring of Lightning and Death itself.' The Outcasts at first prepare to shoot Toothless, but Hiccup stops them out of panic, then covers up his mistake by claiming that crossbows will only make him angry. Hiccup volunteers to display his dragon fighting abilities on the Night Fury, and Alvin happily agrees to watch, telling his men they were about to watch a boy get eaten by a dragon. Hiccup approaches, and Toothless gleefully tackles him and licks him. Hiccup quickly makes Toothless understand the gravity of the situation, and the two of them pretend to fight. While obscured by his body and wings, Hiccup straps Toothless' saddle onto his back. By the time Alvin and his men realize something is suspicious, it's too late, as Toothless turns around with his rider on his back, with Hiccup stating in triumph, "By the way, it's not 'Dragon Conqueror', It's 'Dragon Trainer!"
With this, he and Toothless take off into the air. Alvin realizes he's in a predicament and orders his men to fire their catapults. Toothless dodges all three of the boulders hurled at him but is knocked slightly off balance. In the time it takes for him to recover, the Outcasts readied a volley of crossbow bolts.
Hiccup and Toothless are helpless, but before the bolts hit Toothless, Stormfly incinerates them, as the other teens arrive on their dragons. Stoick sails in range of the Outcast ship and fires his catapults, trying to take out the Outcasts' own catapults. The dragons move in to attack, and Savage fires off a catapult, which goes through the Outcasts' own sail. Although taken by surprise, Stormfly barrel rolls Astrid out of harm's way, but Astrid has no time to hold on, and falls off of her back, landing on Alvin's ship. Alvin quickly seizes her and sarcastically welcomes her aboard. Hiccup sees this and tells the teens to hold their fire. Snotlout misunderstands him and fires a near miss with Hookfang, causing huge amounts of steam as the flames hit the water. Stoick realizes they can take advantage of this and tells Hiccup to get all of the dragons to fire into the water. The dragons create a massive cloud of fog as their flames create steam.
The Outcasts lose their confidence and are intimidated by the eerie fog that blinds them, and hear the dragons' roars through it. Alvin orders them to fire at anything, causing them to attack in random directions. Stoick rams his longboat into the side of Alvin's ship. Alvin is knocked off balance and Astrid hits him twice with an oar. Before he can recapture her, Toothless flies by and rams into his face. With a quick turn, they pick up Astrid and escape. Stoick leaps aboard and begins a fist fight with Alvin, stating it was low of him to kidnap his son, and Alvin replying he will take what he wants. Alvin grabs an anchor line and whips it around in an attempt to kill Stoick, but he gets the anchor stuck in the head ornament of his ship he damaged on an earlier swing. Stoick yanks him forward, and wraps Alvin's wrists with the rope before he disorients him with a punch to the face. The head of the ship detaches and pulls Alvin overboard. Pushing his longboat free, Stoick leaps back to safety and shouts to Hiccup and the others to burn the ship. Hiccup and Toothless begin a deadly diving assault on the Outcast ship as the Outcasts jump overboard. The dragons each shoot at the ship, and soon, they sink it. Hiccup lands on the Hooligan longboat and explains to his anxious father he felt that if he could just get to Toothless he could make things right.
As the kids fly back triumphantly on their dragons, Alvin watches from the beach of Dragon Island, and though he and his men are stranded, having lost to Stoick and his son, he laughs cruelly, saying, "They ride dragons! We get that boy, and we'll ride dragons!" With this, all the surviving Outcasts break out into sinister laughter.
Back on Berk, the crowds cheer for the victorious dragons, welcoming them back to the island. Hiccup happily tells Toothless he's home again. Mildew is the only one who isn't happy, and attempts to remind everyone of what the dragons did earlier (in reality what Mildew framed the dragons for doing), but Stoick tells him the dragons saved everyone's lives, and silences him with a glare, daring him to protest further (and suggesting that Stoick now is convinced of Mildew being the prime suspect). Hiccup follows close behind, and sternly tells Mildew even if he can't prove it, he will never forget what Mildew did by framing the dragons. The dragons and their riders walk happily up from the pier to the cheers of the tribe.
- The title is a reference to the animated music group "Alvin and the Chipmunks".
- Mildew showed it wasn't enough for him, that the Dragons be banished. He also wanted Hiccup gone as well.
- Snotlout somehow managed to lose his first bludgeon into the ocean.
- In this episode, it is revealed that Fishlegs knows how to swim, based on the fact that he didn't drown when thrown into the ocean.
- Snotlout ends up giving his recently found bludgeon to Alvin the Treacherous.
- Alvin throws a sword at the Berkian galley, impaling the dragon figurehead. After the fight sequence between Stoick and Alvin, the sword is no longer there.
- Later in the series, Alvin somehow has the same sword.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Nolan North as Stoick the Vast
- Chris Edgerly as Gobber the Belch
- Brook Chalmers as Silent Sven
- Christopher Mintz-Plasse as Fishlegs Ingerman
- Julie Marcus as Ruffnut Thorston
- T.J. Miller as Tuffnut Thorston
- Zack Pearlman as Snotlout Jorgenson
- Thomas F. Wilson as Bucket
- Tim Conway as Mulch
- Mark Hamill as Alvin the Treacherous, leader of the Outcasts
- Paul Rugg as Savage, one of the Outcasts
- Stephen Root as Mildew