The Master Wraith is the most powerful of the Wraiths in Mordavia. It is encountered at night in Quest for Glory IV: Shadows of Darkness, by traveling five screens south from the Cemetery. It is apparently the spirit of Gregor, or it killed him.
It is unknown how this undead spirit came into possession of the Heart Ritual, however, in the Monastery, in the readable book, it mentions that a person called Gregor has the Heart Ritual but that he has gone missing in the forest.
The Magic User gets a spell scroll.