The Debt Collector by Celia Crown

Rebecca:

He’s big, he’s angry, and he does not have the patience to let me off the hook for whatever I did.
I’m willing to dabble in black magic and call upon Satan himself to sell my soul to him just so I don’t have to be on the receiving end of Mr. Strangely Sexy’s very powerful hands.
Apparently, I owe him money, and he’s going to take it back with interest.
A debt comes with a high price, and he is more interested in me than the money.
He’s going to take everything: my body, my soul, and my heart.
I don’t want to stop him. Not that I can anyway; he’s a brute and a grouchy, old man who takes what he wants.

Derek:

She’s a young, voluptuous girl with a rat’s nest for hair and skittish eyes. She’s ripe for a night of passion under me.
She owes me two hundred thousand dollars in loans, and I have every intention of taking the money back through different means.
I want her to be in debt with me forever. This way, she can’t escape no matter how hard she tries.
What better way to chain her to me than make her pay off her debt through the means of my choice?
Rebecca Shaw will have to get used to this older and stringer man taking control of her life.
Love at fight sight is joke, but my obsession for her is not.