Game of Thrones is a HBO drama series based on the first book in George RR Martin's "A Song of Ice and Fire" series, "A Game of Thrones." In usual HBO style, there's plenty of T 'n' A to counteract the serious literary stuff.
King Robert won the Iron Throne after going to war against the Targaryens when Prince Rhaegar stole the woman he loved, Lyanna Stark, sister of his best friend Eddard. Lyanna dies, and Robert instead marries Cersei Lannister, who he quite plainly despises like nothing on earth. They have three children: Joffrey, who is the type of person that even Ghandi would advocate burning alive, and Myrcella and Tommen, who are too young at the minute to make much of an impact.
Robert also has two brothers: Stannis, who lives in Dragonstone and is hated by pretty much everyone for his stern, fun-hating ways, and Renly, who is universally adored because he's handsome. Nice to see that rule applies in fiction too.
As the series starts, Robert has travelled to Eddard Stark's home of Winterfell, to make him Hand of the King, essentially a role that means Ned has to do all the hard work of running the kingdom while Robert ccan do what he likes best, namely drinking and whoring.
You'd think he'd be grateful for Leonidas' seconds.
The Starks are Wardens of the North, and their motto is "Winter is coming." Cheery bunch. Eddard Stark is the current Lord of Winterfell and newly-made Hand of the King, which at the start of the series requires him to move south to the capital, King's Landing. He leaves behind his wife, Catelyn, and his sons Robb, Bran and Rickon, as well as his bastard Jon Snow, and takes his daughters Sansa and Arya with him.
The Starks are generally honourable to a fault, and basically the only family you'd trust as far as you could throw them.
Who doesn't automatically trust Sean Bean? Well, except for Aragorn.
The Targaryens lost the Iron Throne during Robert's Rebellion. Seeing as their last king was known as Mad King Aerys, this was probably not a bad thing. They were known for marrying their siblings, and also for being able to breed dragons, and use them in battle. Sadly, the dragons are no more and all that's left of the once great house are brother and sister Viserys and Danaerys, who have been on the run since their house fell.
Viserys believes he's the rightful king of Westeros, and you will belive he's an absolute dickhead.
As the series starts, he sells his sister in marriage to Khal Drogo, a Horse Lord with a massive army that Viserys hopes to lead against King Robert.
Probably the most powerful family in the realm. Lord Tywin Lannister is ridiculously rich, and his home of Casterly Rock is said to be full of gold. His daughter Cersei is Queen of the Seven Kingdoms and her twin brother Jaime (who's the image of Prince Charming from Shrek 2) is captain of the Kingsguard, despite killing Aerys, the last king he was in charge of guarding, thus earning himself the moniker of "Kingslayer". Oh, and the twins sort of have sex. A lot.
Incest is a game all the family can play.
The other sibling, Tyrion, is a dwarf. Also a complete badass and one of the more likeable characters in the series, mainly because he's nothing like the rest of his family.
... is much to complicated to even attempt to describe, but suffice it to say it goes on for seven books (two of which aren't published yet) and the fourth book made me cry while I was reading it at lunchtime today.
George RR Martin: The face of evil.
Also, I have no wish to spoil what is truly an amazing production for you, so all I shall say is this: WATCH IT.