This volume of Captain America follows on from the previous volume - The Trial of Captain America - and reprints issues 616-619 of the current captain America comic book.
For those who came in late, Bucky Barnes, Captain America's partner during World War 2, presumed dead in the explosion that put Cap in suspended animation until modern times, was actually rescued by a Russian submarine, and put into suspended animation. Brainwashed and brought out every now and then as an assassin - the Winter Soldier - he was finally able to escape control, and after the death of Steve Rogers, he took on the role of Captain America. After Steve Rogers returned from [spoilers], Bucky continued in the role. Bucky has since been working through his issues, assisted by the Black Widow (who apparently went to the same school for assassins, but somehow forgot to mention it during her time in the Avengers and SHIELD), Commander Steve Rogers (he's been promoted since he died) and Sharon Carter (who also is no longer dead). Bucky's past as the Winter Soldier has since been made public, and he has stood trial for his actions.
The Russians extradited him at the end of the previous volume, for the same past crimes, and this volume relates his life in a Russian prison, where he meets up with a number of failed Russian villains from Marvel history. He can't escape, as he would then become a criminal in the eyes of the USA and the Avengers (read the book), so he has to endure the various plots he uncovers. Meanwhile, in a parallel storyline, his friends in the USA are digging in to the Russian charges against him, but with a noticeably different artist (or inker) from the main(?) storyline, which has the usual high quality of artwork. Steve Rogers comes under increasing pressure to take up the shield again, but manages to resist for now. Eventually the two storylines merge in the climax, and leads us on to the next volume...
There are also a number of `back-up' stories by various artists and writers, gathered together at the back of the book, including work by Howard Chaykin and Paul Grist (see his Jack Staff Volume 1: Everything Used To Be Black And White for his unofficial take on the Invaders!). These are excellent but unrelated to the main story - and may be there to remind people who have dropped in as a result of the film publicity just who Captain America really is.