The Gray Cowl was stolen from Nocturnal by The Gray Fox. I'm guessing Nocturnal's Quest is getting it back. Does it interfere with the Thieves Guild ending? Just wondering...

Would a Moderator please move this to: Oblivion Cheats, Hints, and Spoilers

You guess incorrectly

I don't believe there are any problems doing both in either order.

Your right. I just searched Nocturnal's Quest. Thanks Donner.

I've worn the Gray Cowl while speaking to Nocturnal's shrine. Nothing special happened.

To me, that's one of the odder things in the game-- you're specifically sent by Nocturnal to reclaim a stolen item, so obviously having items stolen from her doesn't sit well with her, but, as Kristoffer pointed out, you can actually stand there and talk to her while wearing the Gray Cowl, which was also stolen from her, and she doesn't even notice.

I guess she's just not the sharpest Daedra Lord around.....

:shrug:

Or perhaps it's because the absence of the item you are tasked with retrieving makes it so that she doesn't realize you're wearing the cowl (although she could have other ways of knowing...).

The lot of them aren't that bright, it seems. Take Molag Bal, for instance: you can kill dozens of his followers, and yet when you come around asking for a favor he apparently doesn't give a damn about it.

:D

"My Eye is returned, and I once again see into.... HEY! What's that on your head!?"

"Ummmm... Nothing???"