From the Module Description:
Thousands of years ago, three different races lived in Aa-chroys "The City in the centre of the Multiverse".
For millennia, peace reigned and prosperity was guaranteed to all. But, in the ways of all things, the City became so prosperous that there soon was overcrowding, and the various Races began to pray to their Gods to deliver them from the Evil of sharing this wonderful space with the others.
So began "The War in Heaven". The Magi prayed to their Primary Gods Larras and Toldas to smite the enemy, the Messengers prayed the message of hate to Rorkar and Wossar, and the Poets likewise to Evandak and Mosrak. Only one of the Pantheon forbade such sentiments, Garrak. The Power of Vines and
Lintels urged the other Gods to stay their Hand, but they did not heed him. So began the "Shadow War", a
genocide of bitterness and hatred.
But even this did not last, for Aa-chroys was soon set about by invaders from somewhere else, and The Lady of Pain and her minions moved into the ravaged area and claimed it for their own. Garrak was cast down and imprisoned in The Maze.
Aa-chroys was renamed "Sigil"; the City of Portals, and there the story was supposed to end… but it hasn't…
An Advanced Dungeons & Dragons 2nd Edition Module for Four to Six players of 6th Level Equivalents