Shadowbane — Erik Scott de Bie

The city of Luskan has always been a den of pirates, thieves, and murderers. But lately, it has gotten even worse. A ship crashes ashore with nothing but corpses. Everyday people go crazy and kill those around them. The only signs found of even the most hardened criminals who walk the streets at night are bones. Luskan's sister city, Waterdeep, has sent a detachment to quarantine the unclean city--to let the filth die, rather than infect the rest of the Realms.

Into this midden of a city disappears the woman to whom Shadowbane owes his life, vanished to a dark and unknown fate. He follows, determined to save her--even if he has to kill every stinking rat in Luskan to do it.