Introduction/What Has Happened Thus Far
The treacherous Robert Baratheon has raised his banner, calling for Prince Rhaegar Targaryen's head, and the North and the Vale stand beside him, and the Riverlands are soon to be wed to their cause. While many ride behind the Stormland's liege, some rest uneasily - torn between their loyalty to King Aerys Targaryen and dismay at his increasingly mad acts.
Under the command of Mace Tyrell, a large force of royalists - men of the Reach - have converged on the ancient castle of Storm's End, trapping Robert's brother Stannis and his men within.
House Cassius of Cider Bridge - a minor house of the Reach sworn to House Fossoway of Cider Hall - was created at the outset of the War of the Usurper when the old lords of Cider Bridge - House Calgar - thought to stymy Mace Tyrell's march on Robert Baratheon. Lord Calgar was betrayed by his sister, Lady Kara, and master-at-arms, Ser Ortan Cassius, and his head delivered to Lord Wylke Fossoway to allow the march of the Reach's forces on Ashford and delivering Robert Baratheon his first defeat.
Having been granted the domains of House Calgar and risen to nobility, Ortan Cassius has led his men to join Lord Mace Tyrell's siege of Storm's End.
All is not well in the newly created house - whispers of opportunism and dishonorable acts taint its founding, the death of Lord Fossoway's son at the wedding of Ortan and Kara cast an ominous shadow over the house's march, families of nobleborn knights that squabbled with Ortan are rumored to have been slain at the behest of House Cassius, and as they join the investment of Storm's End, Lord Ortan's cousin Ser Randyll is found murdered.
Precipitous times await the new house...
Characters will be members of the House Cassius household - be it via familial links or retainers or sworn swords, etc...
Although characters all serve House Cassius (in some capacity), and the siege is led by Mace Tyrell, it is a bit of a lazy siege, so characters should have ample time to pursue some of their own agendas, while also mixing in their actual duties and responsibilities.
A Note About Canon
I hew pretty closely to canon in the set up and motivations of canon NPCs, but I'm not afraid to chart a new path should particularly wild and original schemes get proposed and pulled off. That said, Storm's End is nigh-impregnable, and from the books we know the siege lasts about a year before being broken by Ned Stark.
This does not mean, however, that the ultimate fates of your characters and House are doomed. There will be plenty of opportunity of gold, glory, honour, and yes... intrigue.