omnibus of 2 novels from 1980: Sabella, or The Blood Stone + Kill the Dead.

Kill the Dead (1980) - How can you slay that which is already slain? Yet - sometimes the dead refuse to stay quiet. For there are times when the dead have a duty that must be fulfilled - those are times of horror and haunting. Then one must call the exorcist: Parl Dro, Ghost-Killer. This is the story of 2 sisters who defied him. One was a ghost, and one was not. But which must he kill? Which was the one he must silence?

This is a good place to begin to sample Tanith Lee's storytelling abilities.