A Matter of Honor
Oblivion: Dark Brotherhood Quest
You'll find these orders in a coffin at the entrance to Fort Redman, north of Leyawiin. You'll learn that you're to kill the wandering Alval Uvani. You'll also find a schedule detailing his wherabouts inside.
This elf has a bit of an allergy to honey, so you can try giving him some mead to slow him down. He ocassionaly visits bars, so putting some in front of him increases your chances.
It doesn't really matter how you kill him, as long as you track him down and take him out. Once he's dead, head to the Imperial City Market District. You'll find your 500 gold reward and your next dead drop orders, The Coldest Sleep, in a tree stump there.