From the back cover:
"Glory - or a fate worse than death - in the World of Greyhawk!
The dreadful jails below the appalling City of Skulls, Iuz's nightmare capital, contain many wretched and desperate captives. Among them is Earl Holmer, Knight Commander of the Shield Lands. A brave spy in Dorakaa has shown the way to find and free Holmer - is your party up to the job of freeing him? King Belvor IV of Furyondy believes so. In the way stand fearsome priests and mages of the Lord of Pain; ogres, giants, fiends, and worse hinder the struggle to defeat traps and guardians of Iuz. Plucking Holmer from his grasp will bring great renown, knighthood, and treasure - for those who survive. None has ever escaped Iuz's jails. Who will you be the first to use stealth or storm to breach them?
The City of Skulls presents adventure with a mighty challenge, full of dangers writ large and also unseen (until they strike). This adventure is suitable for 6-8 characters of levels 9-12, and includes pregenerated characters suitable for the quest, player handouts, a unique Notoriety system enabling the DM to draw forth Iuz's most fearsome guardians, a multi-level dungeon-jail, and much more besides. Now is the time for true heroes - is your party skillful enough to survive and return in triumph?"