well u played the game through?
Thats how u find the story, basicly it begins when the Emperor is assassinated, and then continues from there. The reason I ain't writing more is because somebody might actually want that the plot is revealed while he is playing.
And if someone else says the whole story etc (something that u don't learn in the first 1h of gaming) then put something like *SPOILERS* infront of it.
also, google might be pretty helpfull if u want to know the whole story.