The king's brother Roland had gone on an expedition to find a way to reach the Darkside of Xeen. Years later, someone claiming to be Roland returned to Castle Burlock and told the king about an artifact known as the 'sixth mirror'; there were five magical mirrors on the Cloudside of Xeen, and anyone could step into one and emerge from any of the others. The sixth mirror was portable.
King Burlock financed many expeditions to find the sixth mirror, but all his efforts were in vain. Crodo, the king's advisor, discovered that the man claiming to be Roland was actually an undead warlord by the name of Lord Xeen, but Lord Xeen had Crodo imprisoned in Darzog's Tower before he could tell anyone.
King Burlock asked the Defenders of Xeen to find the mirror. The group eventually rescued Crodo and revealed that the mirror had been in Lord Xeen's hands all along. They defeated Lord Xeen, and King Burlock asked the group to follow his brother to the Darkside of Xeen.