My Dark Duke by Kitty St. Claire

In fear for her life, Miss Lillian Hamilton takes a new name and flees to London, desperate to hide from those who wish her harm. A chance encounter with the sinfully handsome Duke of Thorncastle affords Lillian the opportunity to take on a new identity – as his mistress.
Though it goes against everything she believes in, Lillian accepts his offer and finds herself catapulted into a world of wealth, luxury, and pleasure.
As Lillian surrenders her innocence to the duke, she realises that she is faced with another danger – losing her heart to a man who claims to have none of his own.

Sebastian Beaufort, Sixth Duke of Thorncastle learned from a young age that love was merely make-believe. Having spent his formative years attempting to emulate his philandering father, he is finally ready to put an end to his life as a rakehell…until he sets eyes on Miss Mary Smith.
Beautiful, feisty, and charmingly naive, Sebastian is determined to have her under his protection and safe from harm.
As Sebastian claims Mary’s body for his own, he is surprised to find mere pleasure is not enough to satisfy his desire. His ingénue awakes feelings within him, that he did not think he was capable of. Soon, he wants to possess all of her – including the secrets she keeps hidden from him.

As foes from Mary’s past surface once more, can Sebastian find the courage to reveal his true feelings, before it’s too late?