The story revolves around Bucky Barnes (Cap's sidekick from Captain America: The First Avenger), who returns from the apparent dead as a brianwashed Soviet assassin. In all likelihood, somebody will change the "Soviet" part, as it might confuse the timeline somewhat.
“There were always hints [that The Winter Soldier would be the sequel]," Evans said. "The best thing about [Marvel Studios president] Kevin Feige is he’s a fan. He’s not just a businessman, he’s a rabid comic book fan. Even during the first Captain America, well before The Avengers, there were whispers of [The Winter Soldier] being the sequel. So I’m excited to tackle that.”
You can check out the video below, in which he also discusses his affection for co-stars Anthony Mackie (Falcon) and Sebastian Stan (Bucky).
Production for Captain America: The Winter Soldier begins in March 2013.