Spoiler Warning!!!: Plot and/or ending details of a Fighting Fantasy publication follow. Please DO NOT read this article if you do not want foreknowledge of this publication. Although the article below is based on canon, some of its content is considered extrapolation because it assumes a certain course of events through an adventure that has many possible routes.
One of the many rooms of Zanbar Bone's Tower contains a Djaratian-looking sarcophagus which contains the Ring of the Golden Eye (a gold ring with an eye etched into it, long lost, therefore know about it from legends). This ring is in fact a powerful magical item which enables it's wearer to see beyond illusions. Without it, the player cannot defeat Zanbar Bone - as the Night Prince sets an illusionary trap in the room where he is fought - and will be slain and turned into one of Zanbar Bone's undead minions.