Sharon Shinn 
Dark Moon Defender [EPUB ebook] 

The King’s Rider Justin has been dispatched to watch any suspicious activity at the convent that houses the fanatical Daughters of the Pale Mother. Worshippers of the moon goddess, they believe that all magic-wielding mystics are evil. Yet, in their midst, a young novice named Ellynor possesses the gift of healing and the ability to move through the night unobserved. Assuming the guise of a stablehand, Justin befriends Ellynor – and love blossoms between them. And when he discovers her magical talents, Justin will risk everything – his own secret, the trust of his friends, even his very life – in order to save her…