Just found a 400,000 sword.

[Keltiks]

I just stumbled upon the wierdest thing. I was running around Ghostgate and found a place called...well can't remember the name, started with an O. And it is called a Dwenmer training station. Inside I found a bunch of dead dwenmer and then some really really really slow moving dude that hits very hard. Anyway I snuck up on him and talked to him. He mentioned that I could serve him in addition to a hard to find sword called the Keening. Well before I had the chance to serve him, he attacks me. I killed him and on him he had a key. I didn't find any use to this key. Anyway I found this ladder and I went up it into a tower. In this tower was a sword called the Keening and it was like "the sword in the stone". I walked up to it and pulled it out. I checked the stats and it is amazing.

Keening
Short Sword
15-30 damage
Fortify agility, attack, fatigue, and like 4 other things 20-30 points constant effect
Worth: 400,000!!

So I am saying to myself, hells yeah I am a badass. So I put this sword on and it looks so damn cool. (also it said my journal was updated although this wasn't a quest). Anyway, all of a sudden it says, Keening casts a mortal blow on you! After about 3 of these (happened every second) I fell down and died.

Anyone have any information about this quest? Or if you really can serve that big slow powerful monster in that place?
Thanks

[Tkf5000]

its used in the main quest to kill dagoth ur. i belive u need to activate something called wraithguard. i belive u get wraithguard from from vivic. there is anotherweapons too called sunder i think, and its the other weapon used to kill dagoth ur. but im not 110% sure because i havent started the main quest, i just saw a little while reading "prophecies".

[Professor Kaos]

u get the wraithgaurd from vivec, or kill him and talk to the half spider guy in the corpus thing he can make it work, then u can use the sword, too bad i killed him