Shadow of the Rose - Tales of the Black Rose Guard, #4

If you stay with the Lorcan Guard, you will honor your original vow, it is true. But you shall remain forever a shadow of the rose. For as long as she could remember, Sarah had wanted to be a knight. One fated evening, a man with dark eyes appeared at her mother's modest inn, and told her a story of love, loss, loyalty, honor, and a life of which Sarah had only dreamed. Devastated when the man is condemned to the dungeons by her own father, Sarah was told she would never see him again.
She safeguarded his story, and secrets, resigned to them forever being the treasures of her imagination. More than twenty years later, he reappears, offering Sarah an opportunity beyond her wildest dreams. A half-mortal, illegitimate child of a lesser court, Sarah's struggle only begins with leaving all she has known. Her hope for a better future, amid the prejudice of those who look down upon her tainted blood, is maintained by a blossoming love, and being personally trained by the court's captains. An unexpected turn of events gives Sarah an opportunity to change her fate-a position of leadership in the Black Rose Guard.
But to accept will mean abandoning both the man she has come to love, and her vow to Captain Edward. Loyalty and desire clash in one woman's quest to find her place in the immortal guard.