A Knight Amid Thorns by Laurel O’Donnell

The blooming of the rare and mysterious blue rose heralds great change, for when the buds open to full blossom enemies become lovers. Some fear this omen, some desire it. All respect it. Discover the power–and the promise–of the blue rose for yourself.
When the murderer of her brother is welcomed into her castle as a friend, Lady Ella Rames vows to make his life as miserable as hers and to avenge her brother. Struggling to fulfill an oath and find the elusive blue rose, Sir Graden Dumount’s final hope rests with a woman who despises him. Can Ella and Graden overcome their animosity and let the power of the blue rose heal them and turn enemies into lovers?