I tried to teleport back to the mainland when the transport was interrupted and I was accused of murder and theft (somewhat true, but not of that which they accused me of). A guard then came in and reported bandit attacks and pelltar told me to sort it out.
Now Pelltar won't respond to me, Welcar at the warehouses doesn't say anything new. I can't get into the sewers (I just get the new grave message). I keep on going back to the thieves den but I can't find the new thieves. Nothing is happening. A town to the south keeps on being mentioned but I can't get there.
Did you go to the Thieves Den yet? I picked up a walkthrough somewhere here, it said that at the north bridge at the before mentioned location a thief would appear. I will not spoil the rest of the quest, so you're on your own from here on...