Ismae, the protagonist in Grave Mercy, is a survivor type. Seventeen years before, when her mother took an herbal remedy to end her pregnancy, fetal Ismae clung in the womb like a tick and would not be ejected. The consequence of that desire to live is that she was marked with a vivid scar on her back that identifies her as a child of St. Mortain, Brittany's patron saint of death.
When her father tries to marry her off to a brutal man, she fights back and ultimately, ends up on the road to the convent of St. Mortain, where she will be trained as an assassin. Seeing the opportunity to take control of her life, she eagerly embraces the profession of making people dead. (*Shrugs* Why not? Put in the same position, I'd do it. Beats sitting in an office, tap-tap-tapping away, writing a review at Goodreads, because your boring ass office job is making you homicidal.)
When the time comes, Ismae is sent out to do her lethal thing and completes her tasks easily. It turns out, however, that her killings have run afoul of the plans of Duval, the Duchess of Brittany's brother, who is trying to solidify her [the Duchess's] power and wrestle Brittany from the clutches of France. When Duval complains of the convent's interference, the leadership's response is to send Ismae off with him to play at being his mistress. Of course, her real mission is to determine whether Duval is truly loyal to the Duchess and Brittany. If he isn't, Ismae is to push him off this mortal coil.
Duval isn't instantly attracted to Ismae, finding her too young, but throughout the course of the story, he builds a grudging respect that turns to love. No spoiler there, the novel blurb clearly indicates a romantic subplot. Similarly, Ismae is determined to ignore her attraction and focus on her duty. After all, there's no point in getting starry-eyed over someone you might have to poison.
This is probably why I read a lot of YA. It's heavy on the sexual tension, much more subtle, and for me, ultimately, much sexier.
Anyway, for all the romance-y bits, the narrative holds a strong focus on the intrigue, which in turn strengthens the romance (by keeping it from becoming cloying and the over-arching aspect of the plot).
Four stars because while the overall story elements were strong, I found the protagonists a bit humorless and consequently, I didn't fall in love with either Ismae or Duval.