Can't advance, help appreciated

[Dette er Morten. Tur overstått.]

Bought this game during the summer sale and I'm really enjoying it so far. However, I encountered what turned out to be a big problem.

In chapter 3, in the "Following the Thread" quest, you're supposed to explore a bad-boy thug-lair in the sewers. You get the permit/password to enter this area after you've confronted Angus. However, after killing Angus and getting the quest items necessary to enter, I chose the wrong password, causing the thugs in the sewer to attack me. Being low on health, I ran away. When I came back, however, the bandits were no longer hostile, and the option to guess the password or show the letter disappeared. Trying to trigger the combat myself also just results in a conversation, with the one conversation option I'm left with.
Sadly, none of my saves take place before I made this mistake, as I continued doing other quests, hoping this would pass on its own.

Basically: My quest only tells me to enter the lair at this point, although I can't seem to do this through any means (password, combat, or the letter). If there is a way to reset this quest, or if there's another way to enter the Fisstech lab that I've simply missed, I would really appreciate it if you could tell me!