There is an absolute cultist dead body near the potter house, might want to check her body out and see if it's trigger the quest for you.

Councellor Florrick's favorite Warlock.

Back Black Geyser's DLC: https://www.kickstarter.com/projects/grapeocean/black-geyser-dlc-tales-of-the-moon-cult (RTwP Isometric cRPG inspired by BG1).