The Missing and the Missed (2009)

From the front of the book:

In a city built on closely guarded secrets, nothing goes unnoticed—including the strange disappearance of some of the town’s poorest residents. While some remain indifferent to the plight of the missing, a City Watchman is determined to give justice to those who have nothing else. A Living Forgotten Realms adventure set in Waterdeep for characters levels 4-7.