A Storm of Swords is the third in the Song of Ice and Fire Series by George R.R. Martin. It first came out in 2000 in the United Kingdom and then in the United States. It picks up the story lines slightly before the ending of the previous book, Clash of Kings, and features the remaining kings all fighting in the effort to secure their own thrones and secure domination of the entirety of the continent of Westeros. I don't want to provide too much more information because doing so would ruin the surprises (and let's face it, the surprises are the best parts of this series because they truly are gems that you don't see coming at all) but I can say that there are amazing plot twists and fantastic character development that draws you and almost forces you to become attached to the characters without you even realizing what's happening.
What I also really liked about George RR Martin in general, and with this book in particular, is that he is a master at both dialogue and prose. His dialogue is intricate and witty. His prose puts you into the scene and maximizes its use of the reader's senses in establishing scenes and the physical and emotional feelings of the characters that he's writing about. Somehow, Martin also never allows the pace to falter, even as the novel reaches 1100 pages. Definitely go out and get this book, but only after you've read the first two!