Eons ago, Bor, father of Odin, clashes with the Dark Elf Malekith, who seeks to destroy the universe using a weapon known as the Aether. After conquering Malekith's forces, including enhanced warriors called the Kursed, on their home world of Svartalfheim, Bor safeguards the Aether within a stone column. Unbeknownst to Bor, Malekith, his lieutenant Algrim, and a handful of Dark Elves escape into suspended animation.
Five years after the Viking village of Berk made peace with the dragons, they now live among the villagers as helpful companions. Hiccup goes on adventures with his dragon, Toothless, as they discover and map unexplored lands. Now 20 years old, he is being pressed by his father, Stoick the Vast, to succeed him as chieftain, although Hiccup remains unsure if he is ready for this responsibility.
The island of Berk is a remote Viking village, from which dragons periodically steal livestock. Hiccup, the awkward son of the village chieftain, Stoick the Vast, is too small to fight the dragons and instead fashions mechanical devices under his apprenticeship with Gobber the blacksmith, though his inventions often backfire. During one attack, Hiccup believes he has shot down a Night Fury, an extremely rare and dangerous dragon. Hiccup later finds it in the forest trapped in his bolas, but finds that he can't bring himself to kill the dragon and instead sets it free. Stoick assembles a fleet to find the dragons' nest, leaving Hiccup in a dragon-fighting class taught by Gobber. Hiccup returns to the forest to find the Night Fury still there, and realizes it is unable to fly properly because of its crippled caudal fin. Hiccup gradually tames the dragon and gives it the name "Toothless", for its retractable teeth. Hiccup makes a harness and prosthetic fin that allows him to guide the dragon in free flight. By studying Toothless' behavior, Hiccup becomes proficient in subduing the captive dragons during training. Stoick's fleet arrives home unsuccessful, but he is cheered by Hiccup's unexpected success.
In 965 AD, Odin, king of Asgard, wages war against the Frost Giants of Jotunheim and their leader Laufey, to prevent them from conquering the nine realms, starting with Earth. The Asgardian warriors defeat the Frost Giants and seize the source of their power, the Casket of Ancient Winters.
Stanley Ipkiss is a shy and unlucky bank clerk working at the local Edge City bank. He is frequently picked on by everyone around him like the Bank President's son Mr. Dickey, his ruthless landlady Mrs. Peenman, and the mechanics Irv and Burt Ripley who ripped him off. The only exception of this is his Jack Russell Terrier Milo and his co-worker and best friend Charlie Schumaker. Meanwhile, gangster Dorian Tyrell operates a nightclub called the Coco Bongo while plotting to overthrow his boss Niko. One day, Tyrell sends his singer girlfriend Tina Carlyle into Stanley's bank to record its layout, in preparation to rob the bank.
Beowulf (Ray Winstone) is a legendary Geatish warrior who travels to Denmark with his band of soldiers, including his best friend, Wiglaf (Brendan Gleeson). They travel in response to the call of King Hrothgar (Anthony Hopkins), who needs a hero to slay a monster called Grendel (Crispin Glover), a hideously disfigured troll-like creature with superhuman strength. Grendel attacks Hrothgar's mead hall, Heorot, whenever the Danes hold a celebration there, and Hrothgar was forced to close the hall. Upon arriving, Beowulf immediately becomes attracted to Hrothgar's wife, Queen Wealtheow (Robin Wright Penn), who does not love her husband and reciprocates Beowulf's interest.
Ahmad ibn Fadlan is a court poet to the Caliph of Baghdad, until his amorous encounter with the wife of an influential noble gets him exiled as an "ambassador" to Northern Barbarians. Traveling with Melchisidek, his caravan is saved from Turkic raiders by the appearance of Norsemen (presumably Varangian). Taking refuge at their settlement on the Volga river, communications are established through Melchisidek and Herger, a Norseman who speaks Latin. Ahmad and Melchisidek are in time to witness a fight, which establishes Buliwyf as heir apparent, followed by the Viking funeral of their dead king, cremated together with a young woman who agreed to accompany him to Valhalla.
A decade after the events of the first film, Dr. Arthur Neuman is giving a tour of the hall of Norse mythology in Edge City Museum. When Dr. Neuman reaches the part concerning Loki's mask, a man in black becomes increasingly anxious. Dr. Neuman mentions that Loki created the mask and unleashed it on Earth, and that those who wear the mask would have the powers of Loki. When Dr. Neuman mentions that Odin punished Loki with imprisonment, the stranger becomes very angry and transforms, revealing himself to be Loki. The tourists panic and flee, but Dr. Neuman stays to argue with the angry god. Loki takes the mask, but realizes it is a fake. In anger, he removes Dr. Neuman's still talking face from his body and puts it on the mask stand, before getting rid of the guards and storming out of the museum in a whirlwind of rage.
Vicky (Jonas Hämmerle) is the son of Halvar (Waldemar Kobus), chief of the Viking village of Flake. Halvar is a strong and big warrior who measures the strength of people through muscles. Vicky, on the other hand, is a small but very smart boy who always has to prove his father that ingenuity of a man can meet muscles.
A Viking Age expedition arrives in America, intending to slaughter the native "Skræling" population. The party is itself killed by another native tribe, the only survivor being the leader's son, who is adopted by a native woman. The boy is named "Ghost" for his paleness.
Shortly after the death of Charlemagne, a woman called Joan is born in Ingelheim am Rhein. She is the daughter of a village priest (Iain Glen). He also rules his wife (Jördis Triebel) and family with a rod of iron, though his Saxon wife still secretly worships the pagan god Wotan. Even so, Joan grows up to be an articulate girl, who intensively studies the Bible, unbeknownst to her father. After her eldest brother's sudden death, their father wants to send his second son John to the cathedral school in Dorestad, but when the teacher Aesculapius (Edward Petherbridge) visits them in Ingelheim, Joan proves to be far more capable of dealing with the Scriptures than John. Against her father's wishes, Joan is taught by Aesculapius, who introduces her to literary works such as Homer's Odyssey.
A tribe of Vikings feel flustered because in every raid they find their target locations devoid of people. Cryptograf, an advisor to Viking chief Timandahaf, says that the enemies always disappear because "Fear gives them wings". Timandahaf excitedly concludes that they must find a "Champion of Fear", who can teach them to be great cowards so they can fly, making them invincible. The chief says he'll give anything to whoever can bring him this Champion of Fear. Cryptograf hatches a secret plan to seize power and tells the chief they'll find the Champion of Fear in Gaul.
In London in the year 1907, a British aristocrat named Sir Anthony Ross (Donald Sinden) hastily arranges an expedition to the Arctic to search for his lost son Donald. Donald had become lost on a whaling expedition to find the fabled island where whales go to die.
A spacecraft crashes in a lake in Vendel-era Norway. On board is an alien monster, the Moorwen, and the "outlander", Kainan, who activates a distress signal and sets out to trace the Moorwen, which had stowed away on his ship and caused the crash.
The King of Northumbria is killed during a Viking raid led by the fearsome Ragnar (Ernest Borgnine). Because the king had died childless, his cousin Aella (Frank Thring) takes the throne. The king's widow, however, is pregnant with what she knows is Ragnar's child because he had raped her during that fateful raid, and to protect the infant from her cousin-in-law's ambitions, she sends him off to Italy. By a twist of fate, the ship is intercepted by the Vikings, who are unaware of the child's kinship, and enslave him.