Below you will find major spoilers for Thor 2, "The Dark Word," so proceed with caution.
For one, we learn the exact relationship between Thor, Loki, and Jane Foster in Thor 2.
Thor becomes reunited with Jane who becomes possessed by a Dark Spirit, which is connected with the Dark Elves; a race the Asgardians have fallen out with many years beforehand [...] The Dark Elves attack Asgard, and they take a huge hit. So Thor has to rebuild Asgard by putting together an army to go and take the battle to the Dark Elves and defeat them. But the only way he can do this is – he needs to cross over to the Dark World, and the only person who has access to the dark side of Asgard is his old brother Loki, who at the beginning of the film is locked up in prison.
“So what happens is Thor basically has to negotiate this truce with Loki, and he goes on this great trek with Jane, all three of them. They go to this far side of Asgard, which is being shot in Iceland, where they train and assemble an army to go and attack the Dark Elves’ world.”
The first paragraph makes sense as this may describe the Bourne Wood, England battle scene that revealed a huge battle with many different races: "Thor has to rebuild Asgard by putting together an army to go and take the battle to the Dark Elves and defeat them."
Loki is obviously locked up because of his previous treachery, and of course he would know the ways of the Dark World because he traveled them between Thor and The Avengers movie. Remember during Thor he told Heimdall there are more ways out of Asgard etc etc.
We've also heard that a battle takes place between Thor and Loki during Thor 2, that was shot in Iceland, with it said that 500 extras were featured. So this looks to be the case indeed. More than likely Loki either betrays Thor or there is some other disagreement between the two.
Now what is described next was previously rumored, with the death of a major character. Here's the details for that:
But the exclusive twist…is that one of the things that happens during the Asgardian attack is that Thor’s mother gets killed. So it becomes like a vengeance thing. And they were keeping very tight-lipped about what actually happens with Loki, you don’t know whether he redeems himself or he’s still the bad egg.
Now it makes sense why Loki and Thor come to a truce, to avenge their mother's death, but obviously that is not Loki's blood mother, which may lead to the aforementioned brotherly squabble.
Thor 2: The Dark World hammers into theaters November 8th, 2013 directed by Alan Taylor (Game of Thrones), starring Chris Hemsworth as Thor, Natalie Portman as Jane Foster, Tom Hiddleston as Loki, Anthony Hopkins as Odin, Idris Elba as Heimidall, Zachary Levi as Fandral and Jaimie Alexander as Sif, Christopher Eccleston as Malekith the Accursed, Akinnuoye-Agbaje as Kurse.
Head on over to the Cosmic Book News Thor movie hub for images, news and more.
Marvel’s Thor: The Dark World continues the big-screen adventures of Thor, the Mighty Avenger, as he battles to save Earth and all the Nine Realms from a shadowy enemy that predates the universe itself. In the aftermath of Marvel’s Thor and Marvel’s The Avengers, Thor fights to restore order across the cosmos…but an ancient race led by the vengeful Malekith returns to plunge the universe back into darkness. Faced with an enemy that even Odin and Asgard cannot withstand, Thor must embark on his most perilous and personal journey yet, one that will reunite him with Jane Foster and force him to sacrifice everything to save us all.
Starring Chris Hemsworth, Natalie Portman, Tom Hiddleston, Stellan Skarsgård, Idris Elba, Christopher Eccleston, Adewale Akinnuoye-Agbaje, Kat Dennings, Ray Stevenson, Zachary Levi, Tadanobu Asano and Jaimie Alexander with Rene Russo and Anthony Hopkins as Odin, Thor: The Dark World is directed by Alan Taylor, produced by Kevin Feige, from a story by Don Payne (credit not final) and screenplay by Christopher Yost and Christopher Markus & Stephen McFeely (credit not final) and is based on Marvel’s classic Super Hero Thor, who first appeared in the comic book Journey into Mystery“ #83 in August, 1962.
Thor: The Dark World is presented by Marvel Studios. The executive producers are Louis D’Esposito, Alan Fine, Stan Lee, Victoria Alonso, Craig Kyle and Nigel Gostelow. The film releases November 8, 2013, and is distributed by Walt Disney Studios Motion Pictures.