From Introduction:
When the armies of the orcs came to lay siege to this city, they threw themselves against its sturdy walls for months. They clashed against the knights and soldiers who came to the city’s aid, and in the end they were driven off , unsuccessful in their endeavours. They were not able to conquer us. But even though the war is over, not all the orcs have left. Some have stayed behind, lurking in the sewers underneath us. For the ruins of a former age are still preserved down there, and ancient tunnels keep secrets these left-behind soldiers would seek to make their own.
Before this city was build, there was the city before it, and a civilization that no longer exists. Their magicians were all seers and vision-questers, prophets and haruspexes. They could see through the sky and into the realms beyond, divining possible futures and even the machinations of the gods. Of course, even prescient sight could not save their people from the ravages of time, but their works remained long after they were gone. And their secret magics are still there, it would seem, waiting to be discovered be this age’s seekers after knowledge.
These depths have been plumbed by outcasts and mercenary adventure-seekers before, of course. But the city discourages such activities. Who knows what misery they could bestow upon us, by digging up the dangers of the past? But these orcs have lingered down there in secret for many years, growing ever larger and more powerful. With each new tome or shrine or device that they discover, they grow more able both to pursue this quest of theirs and also to affect the city above. In fact, they are not even orcs anymore! Their time beneath the surface has turned them into a kind of troll. Now the city faces a dilemma: if they hire fighters to get rid of these trolls, what if they find something even worse down there?