Iuz built a sinister empire that once held the northern lands of the Flanaess in fear and constantly threatened the surrounding kingdoms in an attempt to rule the entire world of Oerth.

Decades after Zagig (now the Archmage Demigod called Zagyg) achieved his godhood, a powerful mage from the Free City named Mordenkainen led an expedition into the depths of Castle Greyhawk.

Iuz, however, managed to escape the battle and fled back to his kingdom where he could recover his power and plot his revenge against his enemies.

Mordenkainen, barred by oath from entering the dungeons, recruits the band of adventurers to go into the chambers for him and find the secret behind Robilar's treachery.

In fact, entire dungeon levels are left unmapped and the DM is encouraged to improvise their own encounters to fill in areas not covered by the game with their own content.

The work was authored by Jason Bulmahn, James Jacobs, and Erik Mona and is the first significant WotC release of new Greyhawk material since 2002.