Ghostlight / Marion Zimmer Bradley.

Enhanced descriptions from Syndetics:

Ghostlight , this wonderful contemporary fantasy by New York Times bestseller Marion Zimmer Bradley was named "Best Fantasy Novel of the Year" by VOYA when it was first published.

Thorne Blackburn claimed to have magickal powers, to be able to tap into ancient wisdom. Others claimed he was a fake, cheating his many followers out of their money and destroying their free well.

The truth may never be known . . . one dark, climactic night thirty years ago, Blackburn's most powerful ritual went horribly awry, leaving his flock shattered and one woman dead. Blackburn himself vanished.

Now the scattered remains of Blackburn's followers have rallied around a new leader, the charismatic Justin Pilgrim. Hearing this, Thorne Blackburn's daughter, Truth, returns to the site of her mother's death and father's disappearance.

Truth has many unanswered questions. Where are her long-lost half-siblings? Was her mother's death an accident or murder? Is Pilgrim a charlatan, or are his claimed powers real? If he completes Thorne's ritual, will someone else die?

The answers will lead Truth to a deeply powerful truth of her own, one that will change her life forever.