Duchess by Deception by Marie Force

Derek Eagan, the dashing Duke of Westwood, is well aware of his looming deadline. But weary of tiresome debutantes, he seeks a respite at his country home in Essex—and encounters a man digging on his property. Except he’s not a man. He’s a very lovely woman. Who suddenly faints at his feet.
Catherine McCabe’s disdain for the aristocracy has already led her to flee an arranged marriage with a boorish Viscount. The last thing she wants is to be waylaid in a Duke’s home. Yet, she is compelled to stay by the handsome, thoughtful man who introduces himself as the Duke’s estate manager.
Derek realizes two things immediately: he is captivated by her delicate beauty, and to figure out what she was up to, Catherine must not know he is the Duke. But as they fall passionately in love, Derek’s lie spins out of control. Will their bond survive his deception, not to mention the scorned Viscount’s pursuit? Most important, can Catherine fall in love all over again—this time with the Duke?