Lady of Darkness (Lady of Darkness, #1) by Melissa K. Roehrich

Owned by a ruthless Assassin Lord, Scarlett Monrhoe and her two sisters have been trained since they were children to torture and take life. They are the most feared trio on the continent, but they are also wild and unpredictable. A tragic night has Scarlett finding herself locked away in a noble's household, trapped and forgotten, until she is ready to fall in line.

Until the day she is presented with a job. If she completes the assignment, her payment will be something she has coveted for ten years: revenge against the Fae Fire Prince who brutally killed her mother. Is she willing to sacrifice her ideals for retribution?

But when children begin disappearing from her home, all her plans are put on hold as she races to save the most innocent. With the help of old friends, a jilted lover, and a mysterious newcomer who claims the magic of the Fae is possible in the mortal lands, Scarlett delves into the darkest corners of the world. Forgotten secrets will come to light, and she will discover the darkness extends far beyond her own kingdom.