Mirror's Hope - Justine Dowsett Alley

Kind-hearted Mirena Calanais is an outcast in a world where common morality is reversed. She desperately wishes to bring about change and she's given her chance when the 'Avatar of the Light' appears in her bedroom in the middle of the night. Their romance begins, but is tested when Mirena decides that the best way to take on the tyrant who rules their society is to seduce him. Risking it all to get what she wants, Mirena realizes too late that everything has a price and sometimes that price is more than one person can pay alone.