Shades of Cruelty by Sarah Urquhart

When an unconscious raven-haired beauty appears on King’s doorstep, he’s furious to find her on his territory. Who would leave her with a killer like him? He left the mercenary world. But it’s rude to return a gift.
Dark eyes watch her from the shadows when she awakes. Ember Bellamy wants answers King doesn’t have, but she knows he’s a dangerous man. Discovering the man she shouldn’t trust is the one she does.
King never should have retired, but now that he’s keeping Ember, he can’t go back to that life. His secrecy is blown. King is the target and Ember is the prize. He won’t let anything happen to her, even if it means embracing the darkness in his soul and accepting the monster within.