Crimson Desires: Eternally Hers - Midnight Coven, #4

Dark desires. Immortal Passions. An unquenchable thirst for human blood.  Doctor turned immortal, Yelena has resisted the darker side of her vampiric thirst for nearly sixty years. Reclusive, she diligently focuses on her research from her French countryside lab, until an unexpected invitation from the French court thrusts her into the seductive path of Lady Suzette Dieudonnée. A 2, 000-year-old pureblood vampire, the alluring beauty shares none of Yelena's moral qualms.
Falling into a forbidden and tumultuous romance, passions burn through steamy nights as Suzette teaches Yelena she can remain true to her Hippocratic oath while fully embracing her vampiric nature. Along the path of their newfound passion, Suzette realizes she's found her destined mate, but has to convince skeptical Yelena their bond is unique. Together, they must reconcile their love and fears, or be doomed to walk eternity alone. *Crimson Desires is a self-contained story in a shared universe.
Each novel in the Midnight Coven series follows a different couple. Books can be read in any order.*