From the back cover:
This collection of linked adventures takes characters from the Bandit Kingdoms to Furyondy to the Wild Coast, with stops in some of Greyhawk's most exciting locales. But don't be fooled: This is more than just a travelogue.
A dread plague has struck the world of Greyhawk, and the adventurers must travel the length and breadth of the land seeking an explanation and a cure. This is no ordinary plague, but one that seems almost like a punishment—or a test—meted out by some greater power.
Should the characters fail to uncover the secret of this quest, the world of Greyhawk will be forever changed.
This epic campaign provides hitherto unknown details about the cities of Greyhawk and tests each major character class in the AD&D® game.