From the Back Cover:
Centuries ago, a race of humans built an elaborate underground city beneath the Duskmoon Hills called Barakus. These were a magic-loving people, and for hundreds of years they dwelled peacefully in their subterranean home, delving into the arcane arts. Eventually, however, one of their number, a necromancer named Devron, rose to great power and transformed himself into a lich. The wizards of Barakus banded together, and after a great struggle, banished him to a prison far below the city. Before his banishment, however, Devron forged the helm of power, which he could eventually use [to] restore his power.
The Lost City of Barakus, designed to take characters from 1st to 6th level (or higher),m is as much a campaign setting as an adventure. Detailed within these pages is the great, bustling metropolis of Endhome, the Penprie Forest and Duskmoon Hills located north of the city, and, finally, the huge dungeon that is the Lost City of Barakus. Within all these areas are many adventures, NPCs, and locations for the party to explore, interact with and conquer. How and in what order the party chooses to take on the various challenges before them is entirely yours (the Referee's) and the player's choice.