On this page of the guide, you will find a walkthrough for the main story mission - The Dead Man's Voice.
Go talk with Daren and ask about the attack on Constantin's convoy. Go search Catasach's remains - you need intuition 2 for this purpose or the presence of Aphra in the party. Now go talk to MeV, tierny harh cadachtas, to get her help. Then, go with the woman to the place of the ritual.
Go to the specified location, take the ritual weapon Catasacha and take a sample from the scavenger found on the site of the attack. Then create the potion for the ritual and go talk to Mev. Wait until midnight and watch the cutscene.
Now, you must find King Vinbarr. Further progress of the quest will be blocked - you must first complete missions On the High King's Trail and Vinbarr's Sanctuary. You will receive 2000 XP for completing the quest.