Thor: The Dark World is the sequel to Thor and the eighth film in the Marvel Cinematic Universe.
When Jane Foster is possessed by a great power, Thor must protect her from a new threat of old times: the Dark Elves.
Eons ago, Bor, father of Odin, vanquished the Dark Elves led by Malekith, who sought to return the universe to its state before creation using a force called the Aether. Fighting off Malekith's enhanced warriors, the Kursed, Bor contains the Aether within a stone column. Unbeknownst to him, Malekith, his lieutenant Algrim and others escape into suspended animation. In the present, in Asgard, Loki stands before Odin in shackles and is sentenced to imprisonment for his war crimes on Earth, while Thor, alongside Fandral, Volstagg and Sif repel invaders from Vanaheim, home to their comrade Hogun; it is the final battle in a two-year war to make peace in the Nine Realms. In London, astrophysicist Jane Foster, who has not seen Thor in that time, attempts a lunch date with a man named Richard but is interrupted by her intern Darcy Lewis. She takes Foster to an abandoned factory where the laws of physics are upended in spots and objects disappear into thin air. Foster, after bringing her own scientific equipment to the factory, is sucked into a vortex where the Aether enters her.
The Asgardians learn a rare alignment of the Nine Realms is imminent, and at spots where the Realms touch, as at the factory, portals are created. When Heimdall tells Thor that Foster is no longer on Earth, Thor begins a search for her there. She has awakened in the factory after hours in the other realm, and finds herself releasing powerful energy when a police officer on the scene touches her. Sensing the force's unearthly nature, Thor brings Foster to Asgard, but the physicians cannot remove it. Odin realises she is the Aether's vessel and this heralds a catastrophic prophecy. Frigga takes Foster under her wing. In holographic form, Frigga visits Loki in his cell to convey her love and disappointment.
Malekith and his forces, awakened by the Aether's release, turn Algrim into a Kursed and attack Asgard. Malekith and Algrim kill Frigga while searching for Foster, and are attacked by Thor, forcing their retreat. Thor is ordered to remain and protect Asgard rather than pursue revenge. Following Frigga's funeral, Thor decides to take Foster from Asgard to lead Malekith away. He reluctantly teams with Loki, who knows a secret portal to Malekith's world. With Volstagg and Sif guarding his flank, the two commandeer a Dark Elf spaceship and escape with Foster.
On Earth, Lewis learns that Dr. Erik Selvig has apparently gone mad and has been institutionalised after attempting to conduct scientific experiments at Stonehenge while naked. She has Selvig released from a hospital's mental ward with the help of her own intern, Ian. Thor, Loki and Foster confront Malekith and Algrim on Svartalfheim, where, after a hoax in which Loki appears to betray Thor and Malekith takes the Aether from Jane, Thor attempts to destroy the Aether. However, this fails, Algrim batters Thor while Malekith draws the Aether into himself. Loki is apparently killed by Algrim while protecting Thor, but kills Algrim with a Dark Elf weapon. Thor and Foster return to Earth after stumbling upon a portal between realms. The battle shifts to London, where Malekith, in a towering space-vessel, will use the Aether at the exact moment and place the Nine Realms' convergence to destroy the universe and restore the dark-energy state in which the Dark Elves thrive. As Thor battles Malekith, Foster and Selvig use devices they have constructed to shift energy where the Nine Realms meet. At the last moment, they transport Malekith and ship back to Svartalfheim, where the crumbling ship crushes him.
In Asgard, Thor declines Odin's offer to take the throne and tells Odin of Loki's sacrifice. As Thor leaves, the image of Odin reverts to the true form of shapeshifter Loki, who disguised earlier as a warrior, has usurped the throne.
In the mid-credits scene, Volstagg and Sif visit the Collector and entrust to his care the Aether, commenting that, with the Tesseract already in Asgard, having two Infinity Stones so close together would be dangerous. As they leave, the Collector remarks, "One down, five to go". In a post-credit scene, Foster and Thor reunite on Earth.
- Chris Hemsworth - Thor Odinson
- Tom Hiddleston - Loki Laufeyson
- Natalie Portman - Jane Foster
- Anthony Hopkins - Odin Borson
- Jaimie Alexander - Sif
- Rene Russo - Frigga
- Idris Elba - Heimdall the Gatekeeper
- Christopher Eccleston - Malekith
- Stellan Skarsgard - Erik Selvig
- Kat Dennings - Darcy Lewis
- Ray Stevenson - Volstagg
- Zachery Levi - Fandral
- Tadanobu Asano - Hogun
- Adewale Akinnuoye-Agbaje - Algrim
- Jonathan Howard - Ian Boothby
- Benicio del Toro - Taneleer Tivan
- Ophelia Lovibond - Carina