You found a note upon the corpse of one of the half-orc commanders detailing plans to murder Thane Ordlac's wife in their own home.
'Ha! These oafs dare to consider the murder of my wife...and in my own home, no less? Well, we shall just have to make them rue their impudence.
'Speak with Dudsig; he shall give you the key to my home. Go to Lúfa and stay with her. When the villains come to perform their heinous act, you shall dispatch them.
'Nay, do not look at me so! Lúfa is the daughter of Gísling and granddaughter of Gísil, Thane of Garsfeld. My marriage to her sealed the alliance between our houses...how do you think it would look if I were to let her perish at the hands of ruffians? Nay, I doubt not your talents, my friend!'
Dudsig is near the stables in Oserley.
Ordlac has instructed you to obtain the key to his house from Dudsig.
Ordlac's house is near the Oserley stable, on the road to the Mead Hall.
Dudsig gave you the key to Thane Ordlac's house and bade you fulfill your duty there.