Den of Thieves (Ancient Blades 01) by David Chandler
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Born and raised in the squalid depths of the Free City of Ness, Malden became a thief by necessity. Now he must pay a fortune to join the criminal operation of Cutbill, lord of the underworld—and one does not refuse the master . . . and live.
The coronet of the Burgrave would fulfill Malden’s obligations, though it is guarded by hungry demons that would tear the soul from any interloper. But the desperate endeavor leads to a more terrible destiny, as Malden, an outlaw knight, and an ensorcelled lady must face the most terrifying evil in the land.