While Loki was imprisoned,Thor & his companions fought against the marauders on Vanaheim to pacify the Nine Realms. The Asgardians learn that the Convergence,a rare alignment of the Nine Realms,is imminent; as the event approaches, portal linking the worlds appears at random.
In London,Jane Foster investigates what's going on at the abandoned factory where she got teleported to the hidden world where the Aether enters her body. Thor finds her & took her to Asgard where Odin warns that the Aether cannot fallen to the hands of the Dark Elves,who are defeated a long time ago.
Later,the Dark Elf Leader,Malekith,awakened by the Aether's release, invades Asgard searching for Foster. Malekith's lieutenant,Algrim kills Thor's mother,Frigga,who was trying to protect Jane. Thor,Jane,Sif,& the Warriors Three recruits Loki to confront Malekith.
They arrived at Svartalfheim where Loki tricks Malekith into drawing the Aether out of Foster. Sif quickly seals the Aether while the Warriors Three attacks Malekith,but gets overpowered by Algrim. Loki quickly threw Algrim & himself to their death in the abyss. Thor uses his power & summons lightning to strike Malekith,then smashed his skull with Mjolnir,killing him.
With him gone,The Dark Elves are banished back to where they came from. The Aether is formed into a Reality Stone. Thor & Jane return while being watched by a still alive Loki,who impersonated Odin.
Mid-Credits: General Ross is approached by the Leader,who offers him a way to get back at the Hulk.