Valley of the Necromancer Kings

From the introduction:

Seeking to evade capture for his atrocities, Ungoth, the last Necromancer King fled his besieged city of Tyrsis to a desert valley. There, he completed rites to attain immortality; a state the Necromancer King has enjoyed for a millennium. Recently, a coven of cultists led by a triumvirate of evil necromancers (Manse, Darghul and Balagos) have discovered this secret valley. They have moved to the catacombs within and every night, practice rites to renew the reign of the Necromancer Kings. The Triumvirate see their cultist minions as mere fodder to be exploited as they see fit.