Daindreth's Assassin. Daindreth's Assassin, #1

Born to be a sorceress. Cursed to be an assassin. Chosen to be his empress. Magic has two immutable rules-every spell requires a sacrifice and every curse can be broken. Amira Brindonu is a sorceress turned assassin, bound in a curse that forces her to obey her father, even to the point of high treason. When he orders her to kill the future emperor, she fails, but discovers a secret that could bring the whole of the empire to its knees. The archduke is stricken by a curse that could sentence him and his people to damnation, but Amira could be the only key to breaking it.
In a desperate last-ditch effort, the archduke takes Amira prisoner and makes a pact to protect her from her curse if she will help free him of his own. As time begins to run out, Amira soon learns that there are enemies that blades can't touch and there are fates worse than death. Caught in a web of sorcery, intrigue, and her growing feelings for the archduke, the assassin must decide just how much she is willing to give to save the only man she's ever loved. Every curse can be broken, but can two cursed people save each other?