Main Quest (Oblivion)

The main quest of TES: Oblivion is that the Emperor Uriel Septim IV is assassinated by attackers unknown, as well as the three Doppelganger heirs of Uriel Septim IV. It is up to the player to find the long, lost heir of the Emperor and to return him to the throne and close shut the Marble Jaws of Oblivion.
 * Possible Spoiler*