Downshadow

In the underbelly of the City of Splendors, a lone vigilante is sworn to rid Waterdeep of its most nefarious citizens
 
Watchman by day, vigilante by night, Shadowbane keeps to himself as he surveys the labyrinth beneath the city of Waterdeep. It is his duty to ensure safety and order in his city, and he knows all of Waterdeep’s secrets.
 
However, when a young woman—frightened and fleeing from unknown danger, with no idea of the hidden powers she possesses—arrives in the city, Shadowbane uncovers a secret plot, previously shielded even from his watchful eyes. When his friends start dying and the girl is kidnapped, Shadowbane must choose between the darkness and the light in his heart: to avenge the deaths of his friends, or to let the villain live to face—and possibly escape—justice.

Downshadow is the third book in a series of standalone novels set in Waterdeep and the first book in the Shadowbane series.