Saga of the Witch Queen

From the publisher:

Drawn into a series of adventures spanning the north, the heroes take up arms against the sinister machinations of Kyleth, the Witch Queen. Beginning in the miserable bog known as the Great Swamp, the heroes are called to thwart Kylethís plot to create sinister artifacts of unholy blight. But the Witch Queen is a tenacious foe, protected by wicked dweomers and ancient rites. Running their prey to ground, the heroes must navigate the perilous halls and torturous caverns of the Lost Passage of the Drow. Their epic quest comes to a head in a battle that stretches across the icy reaches of the Northlands and to the stygian demesne of Baba Yazoth herself!