The novel opens in the wake of the greatest storm to sweep through the Barbarian Archipelago in more than a century. Camicazi was lost while sailing through the storm and both the Bog-Burgulars and Hairy Hooligans search for her in the dangerous and inhospitable Eastern Archipelago--home to the haunted beaches and both the slavetrading Uglithug and crazy Berserk tribes. Unfortunately, darkness creeps up on them and the Hooligans are forced to find a suitable spot to camp until morning. While searching for said spot, they see a mysterious object on the beach and investigate, Stoick inadvertently causes his boat to run aground and sink and the tribe is forced to camp in Uglithug territory on a beach that is supposedly haunted; the mysterious item turns out to be a spooky ancient throne covered in Hooligan ruins that washed ashore in the storm. As they settle down for the night, Stoick reassures them UG the Uglithug, the merciless slavetrading chief of the Uglithug tribe, rarely visits the beach where they camp because he believes it to be haunted.
However, Stoick is wrong and Ug and his men savagely wake the Hooligans in the middle of the night at swordpoint. After making wild accusations Stoick is trying to steal his lands, UG reveals this to be a joke and informs Stoick he actually came to discuss an entirely different and unexpected matter: someone from the Hooligan tribe wrote love letters to UG's daugher, Tantrum O'Ugerly, a crime punishable by death. UG brings out his daughter and reads the letter, telling the Hooligans he will kill all of the unmarried boys and men if the culprit doesn't come forward. Hiccup deduces Fishlegs is responsible for the letters and lies claiming he wrote them to save his best friend; only the son of a chief may write love letters to a chief's daughter or risk certain death. As he endures ridicule and surprise from his fellow tribesmen, UG presents Hiccup with the Impossible Quest to win his daughter's hand, as per viking tradition--collect honey for mead from the bees of Berserk.
Stoick brings all of his warriors on the quest to increase Hiccup's chances of survival and the boys train immediately. However, during one of the training exercises, Fishlegs sustains a bump to the head and his Berserk traits emerge. Hiccup escorts him home and returns later to discover Fishlegs has gone by himself to Berserk to find his parents and prove he is a hero worthy of a chief's daughter. Hiccup immediately goes to the aid of his friend, knowing the quest is a suicide mission and his friend is unwell. Hiccup stumbles upon a crashed Fishlegs and his chickenpoxer in the forests of Berserk with a bag full of Berserk honey and covered in Scarers, small, blind dragons that rely on fear to find prey, his Berserk mood having worn off. Hiccup attempts to rescue Fishlegs but the chickenpoxer spooks and flies away with Fishlegs still on its back, Hiccup chases his friend and both are ambushed by Poison Darters, dragons in the service of the Berserk chief that shoot tranquilizing darts.
The two friends wake up after being captured by the Berserks, the chief assumes they are both fiances of Tantrum and sentences them to be sacrificed to The Beast, along with the other eleven fiances, later that night. Hiccup discovers Humongously the Hotshot Hero is among the imprisoned fiances and is the one Tantrum claims she loves. Hiccup tries to convince the suspicious French cook, Alphonse, to help them escape, only to discover the cook is his arch nemesis, Alvin the Treacherous. Alvin agrees to help Hiccup escape in exchange for his own freedom and the prospect of killing the boy, but Alvin tricks him and traps Hiccup in an inescapable prison cell made to look like a tree. Hoping to share a cell with Camicazi, Hiccup quickly discovers he's in the presence of something much more sinister; his cell-mate reveals herself to be a witch named, Hogstrude, and he tells her his name is Fishlegs. At the same time, he discovers Toothless is close to death after he ate Stoick's "magic" magnetic ball and various other inedible objects. Hiccup begs the witch to save Toothless, claiming he's UG's (her captor) favorite dragon, the witch agrees but only in exchange for the spoon in the dragon's belly. To Hiccup's amazement she performs successful surgery in complete darkness and saves Toothless' life. Both the witch and Hiccup guess they each gave the other false names and agree to a battle of wits to guess each other's true identity, with the victor winning the right to kill the other. The witch tells Hiccup the reason UG imprisoned her and tells him the tragic story of the last King of the Wilderwest and his ancestor, Hiccup Horrendous Haddock II. Hiccup's interest in the story and his ancestor gives away his identity, however he also correctly guesses the witch is Alvin's Mother, after she reveals she thinks Alvin is the heir to the throne of the Wilderwest. Hiccup discovers a strange key in the pile of things that came out of Toothless' stomach and unlocks his cell, narrowly escaping from the witch.
He searches for Camicazi and with the aid of a recovered Toothless discovers a trail of winkle shells that leads him to his friend. After freeing her, they rush to save the rest of the captives before it's too late. Hiccup locks himself back in his cage, much to Alvin's surprise, and is first to be fed to the beast. However, he discovers The Beast is none other than Furious, the dragon-brother of his relative, Hiccup Horrendous Haddock II. Hiccup reveals his identity but is disappointed to discover after years of torture and the death of his human-brother, Furious is full of nothing but hatred for humans. He frees Furious and binds him with an oath of words he will help Hiccup free all the prisoners on the island and never harm humans. With the aid of Furious, Camicazi, and the freed fiances, Hiccup releases every prisoner on the island. Furious goes back on his word and sets the island ablaze, promising Hiccup he will return in a year's time with a dragon rebellion and kill every last human. While escaping, Hiccup briefly swordfights with Alvin and his mother amidst the flames, however both are seemingly consumed by the fire and the Hooligans rescue Hiccup, along with his friends.
The story ends with the Hooligans and Bog-Burgulars having a breakfast to celebrate the safe return of their heirs and Humongously Hotshot sailing away with his new bride, Tantrum O'Ugerly, having borrowed Hiccup's key to steal her away in the dead of night. Humongously Hotshot returns Hiccup's key, Stormfly, and retrieves the throne of the Wilderwest to show his gratitude. As the young heroes recover from their latest adventure, Hiccup reassures Fishlegs there will be other loves while secretly hoping that Furious can also find it in himself to love again...
- Hiccup Horrendous Haddock III
- Alvin the Treacherous
- Excellinor the Witch
- Berserk Chief
- Ug the Uglithug
- Stoick the Vast
- Big Boobied Bertha
- Snotface Snotlout
- Hiccup's Windwalker
- Fishlegs's Chickenpoxer
- Poison Darters