I'll load a save and see what I can do. I think you're just missing some quest-essential crap.

Check Dandelion's entry in your journal in the meantime - perhaps you've overlooked something?


Edit: Okay, I did a little snooping around in a save of mine and found some stuff out:

Firstly, I do not recall the "Will-O-Wisp" being in this quest at all (or even remotely related).
Once Bras of Ban Ard deciphers the notes, you take them down below the city to the sewers (which are right next to The Mighty Numa, according to the wiki) and then speak to the guardian door. I believe the Will-o-wisp of which you speak is almost directly above (in terms of altitude) the guardian door. You need to go beneath the city. Once inside, the quest progresses as usual, with some puzzling puzzles and some combative combat.

Hope that all helps.

I'm pretty sure the will-o-wisp and the Guardian Door you mentioned are the same thing. Is what you're talking about simply a human face made from fire?

Alright, I figured it out. Turns out I had overlooked a dialogue option when speaking with Bras of Ban Ard. The optioned mentioned a manuscript, which I though was referring to the manuscript in the Encrypted Manuscript quest, when in reality, it was referring to Malget's Notes.