From the back of the book:
As the Third Age came to a bloody close, one of the first victims of the brutal march of the Shadow's armies across Eredane was the city of Highwall. Since the First Age, the city and its Scholar's Academy stood as a beacon of hope and enlightenment in a darkening world. That shining beacon was shattered seemingly overnight as the fury of the Shadow in the North descended on the world.
Now, a hundred years later, the city of Highwall lies in ruin. At the center of this desolation rises Theros Obsidia, a black tower of impossible size that was magicked from the earth and stone like a splinter drawn from flesh. This is the locus of Izrador's power in Eredane and the fortress of his legates, the Order of Shadow. Huddled around the tower are the camps and garrisons of the Shadow's hordes, along with the ruins and hovels of the city's survivors. Highwall has become a place of death and darkness, and only the bravest, most foolhardy, or most desperate heroes dare to intrude into the heart of Shadow.
The fourth supplement for the award-winning MIDNIGHT campaign setting, City of Shadow offers detailed information on the ruined and occupied city of Highwall, a level-by-level description of Theros Obsidia complete with beautiful maps and illustrations, and in-depth information on the Order of Shadow.