Shadows Return : The Nightrunner Series, Book 4 (Nightrunner)

After a victory in Aurn︠en, master spies and dissolute aristocrats Alec and Seregil accept a new assignment that takes them to Seregil's homeland, only to be ambushed, separated, and sold into slavery, where Alec's unique heritage entangles them both in a dark realm of alchemists, madmen, and an inhuman creature that may be either a monster or their only hope. Original.