Despite it being the next film to go into production, word on the "Thor" sequel is still pretty much under wraps, with the title announcement the only part of the presentation that really referred to the film. As best as we can tell, 'The Dark World' doesn't refer directly to any existing part of the "Thor" comics, although it could be a reference to Dark Elves, a powerful race who've been recurring Thor villains since the 1980s, ruled over by the evil Malekitch the Accursed, along with his right-hand man Algrim The Strong (later transformed into a more powerful being called Kurse by super-powerful villain The Beyonder). Rumors have pegged popular villains The Enchantress and The Executioner (the latter thought to be the one that Mads Mikkelsen was in talks for before dropping out) to be the antagnonists in the sequel, but could the Dark Elves be the real villain here?
Unlike with "Thor," Marvel were a little more revealing with their subtitle for the "Captain America" sequel, making it pretty clear where the plot will be heading. The Winter Soldier is an alias of Bucky Barnes, Cap's best pal, as played by "Gossip Girl" star Sebastian Stan in the first film, and last seen falling off a train to his apparent demise. In the comics, Bucky seemingly perished in the same incident which freezes Steve Rogers, but in a recent plot twist written by Ed Brubaker, it turns out, in fact, that his body (minus an arm he lost in an explosion) was found by a Soviet submarine, and taken back to the USSR, where he's rehabilitated, albeit with a total loss of memory, and trained to be an assassin.
Kept in cryogenic stasis between missions (hence not aging much), Bucky, codenamed The Winter Soldier, becomes a ruthless killer (and at one stage, has a relationship with Black Widow, suggesting we might be seeing Scarlett Johansson cropping up in the film). He finally crosses paths with his old friend after killing hundreds in a terrorist attack in Philadelphia in the present day, stealing a Cosmic Cube, and kidnapping Sharon Carter, SHIELD agent, and niece of Cap's wartime love Peggy Carter -- indicating that Hayley Atwell may have another role in the follow-up. Rogers eventually confronts Bucky, bringing back his memories, and, feeling guilty for his past actions, he teams up with his old friend, and joins S.H.I.E.L.D. In the comics' continuity, he actually takes up the mantle of Captain America after Steve Rogers was assassinated, but that would be a fairly bold move for the film to take.
Either way, it seems like we're looking at an extended role for Stan in the film, although we suspect that it won't be strictly villainous, with another baddie -- a returning Red Skull? Arnim Zola? Baron Zemo? -- pulling the strings behind the scenes. Either way, it gives a nice emotional heft to the plot, which can only be a good thing.