The High Priest of the Cult of Drugoth, Ugarad the Harbinger, must still be in Bagud-dum.
'The one who was leading that ritual must be the High Priest of this \qCult of Drugoth,\q and I'll wager he's still in the fort. I warn you: he might be quite powerful, and perhaps too powerful for you to take on alone. But if you feel up to it, perhaps we should take him on now.
'After all, sometimes evil only grows in power, rather than declining in it....'
Ugarad the Harbinger can be found somewhere inside Bagud-dum.
You should defeat Ugarad the Harbinger.
Hórin can be found outside the dwarf-fort Bagud-dum.
You should talk to Hórin.
If Hórin is no longer at Bagud-dum, he can be found at Fellgát.