Help with final thieves quest

[klestor]

I went through it, thought i grabbed the thing but I guess i didn't.  But yet my quest arrow points to grey fox.  I can't remember where the beginning sewer is, and don't even know if the it is still there.  If someone can tell me how to get in there, or even better if they know the item id so i can just add it to my inventory, or point me in the direction of somewhere with a list of all the items to add, and maybe i can look for it...