The story begins in Cyrodiil, the capital province of the world of Tamriel. The emperor has been killed by an unknown assassin, and the throne is empty and waiting for the heir. Without a true emperor the gates of Oblivion open and Tamriel is in great danger as the demons attack Cyrodiil. It is your mission to find the heir and save what you can.
Oblivion is featured with a new AI system, namely Radiant AI. This new AI gives non-player characters a choice of their own. Depending on circumstances and characteristics they make their own decision on when they go to church, talk to you, steal etc. The game has also plenty of guilds that can be joined and advanced without completing the main quest. All these guilds feature a unique storyline.