Elder Scrolls IV: Oblivion - Knights of the Nine

Description:
The Gods have forsaken Tamriel. A fallen King has been unchained from the darkness of Oblivion to seek vengeance upon the Gods who banished him. Only a champion pure of heart can vanquish the evil that has been released upon the land.

Heed the call, reclaim the lost relics of the Divine Crusader, and return the Nine to glory. New dungeons, characters, quests, and mysteries await in the Knights of the Nine.

Begin a New Faction
The Knights of the Nine have long been disbanded. Reclaim their former glory as you traverse the far reaches of Cyrodill across an epic quest line.

Battle New Foes
Encounter Umaril, the ancient Ayleid Sorcerer-King, and his minions, the fearsome Aurorans.

Discover Unique Items
An entirely new armor set and weapons, each with unique powers, are within your grasp … if you are worthy.

Unlike other downloads, this quest is integrated directly into the game. The Knights of the Nine is like any other faction, you join by hearing rumors and talking to people. After the download, go to the chapel in Anvil and talk to the guy outside … this should get you started.