Surfaces by Ann Denton

I made a terrible mistake.
I gave my heart to my worst enemy in order to survive.
Relinquishing my heart allows me access to my pent-up magic. But it has a side effect. Now, as I swim through the sea kingdom, I find myself randomly consumed by dark thoughts.
Sometimes when I stare at the men competing in the tournament for my hand, I get a random itch—the urge reach out and snap their necks. To hear that brittle crack of bone and watch their eyes fade to gray. It doesn’t matter how sweet, funny, or handsome they are. The desire to hurt them is nearly overwhelming.
I always thought my birth mother was a monster by choice. Now, I wonder if it’s not a sea sprite’s destiny.
Will I become a leviathan too?
I need to know, and I need to find out quickly as these men grow closer to me and my evil appetite grows stronger. I don’t know what I would do with myself if I hurt the sweet courtier, Keelan; the dashing pirate, Valdez; or my one true love, Mateo.
I’m afraid that they’ll see what lies beneath the surface, the shadows swimming in my eyes.
This beast inside might not just cost me my kingdom, but my soul.