Heart’s Rescue by Meredith Hart

Everyone knows the Lands Below belong to the monsters.
When my beloved prince vanishes in a noble attempt to rescue his sister’s heart from the Lands Below, I have to go after him. It’s what any woman would do for the man she’d been raised to marry. Besides, rescuing the prince should be enough to finally force the king to agree to the union my parents have been planning since I was born.
But the frozen Lands Below are nothing like I expected. And Rowan, the brilliant and bitter sentry who’s now my only hope of finding my way back to the Worlds Above, possesses strange, terrifying magic that’s made him an outcast. Even in the land of monsters.
And the worst part is, I’m starting to like him.