Oblivion was the follow up to Bethesda’s Morrowind
and brought huge improvements for the time. The game takes place in the Province of Cyrodiil, home of the Imperials.
The main story involves a few things:
1: The Emperor, Uriel Septim VII, was assassinated by the Mythic Dawn cult
2: Before he dies, he entrusts you, a nobody who was rotting in prison at the beginning of the game, to find an heir
3: Because there is no heir to the throne, an old covenant is broken and gates to Oblivion have sprung up around with Daedra invading
4: Stopping Mankar Camoran, the Daedric prince that the Mythic Dawn worship, from taking over