Deeds of Men — Marie Brennan

A young man lies dead in a Coldharbour alley. Before his death, he uncovered secrets that could threaten the mortal world above and the faerie world below. Now, to find the murderer and protect both realms, Sir Michael Deven will need the help of a man with reason to hate the fae of the Onyx Court -- the victim's own brother.

A novella of the Onyx Court, set between Midnight Never Come and In Ashes Lie, in the years 1621-1625.