Heart Thief by Ker Dukey

Monsters come in many forms.

Some want shiny new toys to play with—others want blood.
Mona Walters dreams of adventure, of a world beyond the shoreline she’s confined to. She yearns for vibrancy in her dull, mundane existence, but succumbs to the bleakness.
Until the necklace her sister wore the night she was brutally murdered shows up on her door wrapped in a neat bow, fueling her to run away and seek out the person responsible for stealing her sister’s life.
Mona wished for more—for color in her gray world.
What she didn’t realize was just how much more she would get.
And that the world outside her own was soaked in red—blood red.
The world she dreamed of is made of nightmares.
A rich, influential world of two brothers—and once they have her in their sights, they plan to keep her there.
Her father kept her secluded for a reason.
Be careful what you wish for.
There’s a thief out there, and he’s coming for Mona’s heart.