The Flame and the Shadow — Denise Rossetti

Some are drawn to the light.
Some are drawn to the dark.
Some desire both...

Grayson of Concordia, known on countless worlds as the Duke of Ombra, is a mercenary, a sorcerer of shadows--a man whose soul is consumed by darkness. For Gray, the bleak savagery in his heart is manifest in an entity he calls Shad. He has long resisted Shad's enticements, but when he is hired to kidnap a fire witch, he seizes the chance to restore his soul--no matter the cost.

Cenda's heart is ash. Since the death of her precious baby daughter, life has lost all meaning for the fire witch. Slowly, she has worked to master her powers and go on living. But when she encounters Gray, her will is no match for her desire. But her love may not survive the terrible discovery of Gray's betrayal...