Forbidden Mistress by Evelyn Austin

Cassie Fitzgerald has long been my secret obsession, one I never meant to act on.
She’s a broke college student who just lost her job, so I devise a solution for us both—a lucrative job at the elite sex club, Obscura. There, my real identity is hidden behind a mask. There, I’m a Dom called Hart. There, in the darkness, I command her body, fulfill her darkest desires…and make her mine in every way.
But if she ever discovers the truth about me, I’ll lose her forever. Because beneath the mask, I’m the man she hates most…
I’m her stepbrother.