I think it's "Thorak" anyway, the Vergen "runesmith". You have to speak with him about his making a custom chalice for Saskia (which may have been rigged to deliver poison with some kind of hidden mechanism). But you can't do it! Once this mission becomes active, "Thorak" becomes impossible to speak to! He's there, but the UI just won't "select him" nor bring up the "talk command"!

Or can you just ignore this?

Didn't have a problem with this 1 either.

There are 2 quests involving Thorak, Suspect Thorak and Baltimore's Nightmare.
Suspect Thorak involved the chalice and activated during Royal Blood.
IIRC you might get stuck in ST if you didn't finish BN first.

I finished BN off, I went for the "let him off the hook" option.

I killed him. Had no problem with the SN mission afterwards.
Only weird thing I remember from 1 of those 2, was I had to talk to his assistents, but could only talk to him.