It is a precipitous time in the Westerlands. Lord Tytos Lannister is kind, but his abilities are less than what the Lion needs, and many take advantage of him or mock him in their cups. Lords ignore his orders, often doing as they will. Many debts owed to him remain uncollected, gold that should return to Casterly Rock. Bandits flaunt his lack of authority, plaguing the lands. In an attempt to reassert his wealth, power, and influence, Lord Tytos has arranged a tourney at Casterly Rock, where he intends to announce the betrothal of his young daughter, Genna.
Beneath the shadow of the Rock, the other Houses of the Westerlands make their moves - currying favor, arranging marriages, repaying debts, and seeking revenge - all hoping for 'A Reign of Gold'.
This game will be using the 'A Game of Thrones' campaign play style, where each player will create and control their own noble House situated in the Westerlands of Westeros, and a stable of characters associated with that House. Although it is not necessarily going to be player vs player, that is entirely within the realms of possibility - and sometimes hurting one of your rivals is the easiest way to improve your own House, but solid alliances bound with marriages can strengthen both Houses' statuses in the realm.
Generally speaking, each House will have 2-4 PC level characters (depends on the House's influence resource), but in any given story/chapter, only one will be used as a primary character. That said, it is entirely possible that a given House may send off characters on side missions, which means that you could be running different characters in different stories/chapters at the same time. All secondary and tertiary characters in the House will be NPCs run by me, so although you'll have control over your house, the possibility for internal conflict still exists.
*Note: There will decidedly be no niche protection or what not in this game. Since each player will be controlling their own House, it's very possible that each may have an incorrigible schemer, a dastardly knight, or a repentant bastard septon. Unlikely, but it could happen. Standing out may come down to how adept your own plots are, and if you can out-clever your rivals.
The game begins in the year 253 after Aegon's Landing (about 44-45 years before the books). King Aegon V the Unlikely sits the Iron Throne, Lord Tytos Lannister is Warden of the West in Casterly Rock, and his son and heir, Tywin, is a mere boy of 10. I expect most stories and plots to stay within the Westerlands, but depending on your own actions, things could easily spill over into the Reach, the Riverlands, the Iron Islands, or wherever.
I try to hew fairly close to canon where I can, but the game comes first, so if you pull off some grand scheme, then the books be damned. As a note, the Reynes and Tarbecks would not have been wiped out yet; whether that proceeds on schedule or is averted (or happens sooner), may very well be up to you players.