Delcairn Sebastian has asked that I use the information that Thavian provided The Brotherhood to prevent Revlos from doing any further damage. Thavian learned of a short meeting that I can listen in on that will clue me in as to the location of Revlos' debriefing. I should purchase some poison called Fate's Whisper, listen to this conversation, and then poison the cups that will be present for the debriefing.