Eons ago, Bor, the 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 him, Malekith, his lieutenant Algrim, and a handful of Dark Elves escape into suspended animation.
In present-day Asgard, Loki stands imprisoned for his war crimes on Earth. Meanwhile, Thor, alongside warriors Fandral, Volstagg and Sif repel marauders on Vanaheim, home of their comrade Hogun; it is the final battle in a war to pacify the Nine Realms following the reconstruction of Bifröst, the "Rainbow Bridge" between realms, which had been destroyed two years earlier. In London, astrophysicist Dr. Jane Foster's intern, Darcy Lewis, now with her own intern, Ian, takes Jane to an abandoned factory where objects have begun to disobey the laws of physics and disappear into thin air. Separating from the group, Jane is teleported to another world, where she is infected by the Aether.