Bride by Midnight. Columbyana, #10

A Bride's Curse Romantasy Lyssa Tempest is desperate to find a husband. A witch's portent years past made it clear that if she didn't wed before the age of twenty-three she would not wed at all. Lyssa doesn't want to live her life alone, so after her fourth failed wedding, on the eve of her birthday, she goes on a late night hunt for a man. Any man. And she finds Blade Renshaw. Blade is in the capital city of Arthes with murder his only goal.
The pretty and naive Lyssa is a means to an end, his way into the well-guarded palace where he can, at last, avenge his sister's death. He doesn't intend to care for Lyssa, perhaps even to love her. They are not prepared to face Lyssa's newly awakened powers or their part in a coming war, as Ksana demons and the man who would lead them watch and plot against the witch and the blade.