An Unwanted Hunger, by Ciana Stone, is free in the Sony store, courtesy of romance/erotica publisher Ellora's Cave. Available to Canadians and presumably also US persons. This is apparently the 1st book in the Soul of V'Kar series.
Description
Passion this strong is dangerous. They both know it. Mortal enemies, their respective factions have been at war since the dawn of man. Resa is a Dhampir, bred and trained to hunt Vampyres. Constantine is a prince among the Vampyre, the oldest and most lethal.
Nothing good can come of this hunger, this need that drives them relentlessly toward one another. Neither reason nor devotion to duty can stay their need. There is but one way to quench the thirst that drives them. Once sated, they can return to the battle and see which one, if either, is left standing.
But one drink from the cup of desire serves only to magnify the hunger. One act of lust that could alter them forever, changing the course of destiny.