The Dark in Her Veins by M.K. Lobb

From critically acclaimed, bestselling author MK Lobb comes a noir romantic fantasy set in a world in which sin is a fatal disease, and the rich hire the poor to carry out their basest instincts―until the forbidden romance between a sinner and a mysterious figure threatens to destroy everything.

In Valestadt, everything has a price. Sinning leaves its mark in the form of the Bloodrot, a slow-creeping disease that leads to madness, then death. Most sins are negligible, but murder―committed enough―can be fatal. For the rich, violence is something to be outsourced. For the poor, it's a paycheck that comes with a cost.

Talin Keller is a sinner. Employed by  the holiest man in the city, the Prophet, she gets her hands dirty so his can stay clean. And with her Bloodrot rapidly advancing, Talin knows her next job could be her last. But when a new assignment puts Talin on a collision course with a shadowy figure known as "the Warden," she begins to see a future for herself that doesn't involve a body bag. If she can get close enough to the Warden, she can trade his life for her own freedom. That is, if she can keep her balance on the knife's edge. 

The closer Talin gets to the Warden, though, the more she finds herself falling for his sharp edges and twisted sense of justice. As savior and sinner bleed together, Talin finds the real threat isn't either man – but a conspiracy tied to the past she hoped was dead.