The adventure takes place in the Underdark, and begins when the players are captured by Drow Elves. They escape with a group of other prisoners to find that demons have a stronger influence in the Underdark than expected. As they travel between locations searching for an exit from the Underdark, they discover that various demon lords including Demogorgon, Zuggtmoy, and Juiblex, have been unleashed. They escape, but are called back by leaders in the Dwarven settlement of Gauntlgrym. The players are then tasked to lead a war band through the Underdark in an effort to stop the demons from destroying the world. The adventure ends when the players pit the demon lords against each other before finishing off the remaining wounded ones.
