Too Wicked to Woo by Tammy Andresen

He’s dark and dangerous and so delicious, how can she resist…
Miss Penny Clearwater considers herself a sensible woman. After all, she’s navigated her mother’s death, her father’s financial ruin, and her own fall from society with all the grace she could muster. So when her friend, Lady Chloe Dryden suggests they make a chronicle teaching young ladies of London all about the elusive rake, Penny refuses. It’s a silly idea that could end in absolute disaster. Except, she’s almost nothing left to lose. And when the perfect rake crosses her path, why not do a little research on Lord Preston? So he’s handsome and dashing… she’s only interested in the book, of course. Isn’t she?
Lord Wesley Preston hasn’t had much by the way of successes since he left the military. A failing earldom, a bad accountant, and a drinking habit have left him in tatters. He desperately needs a break. And when Miss Clearwater stumbles into his life, he discovers that she had just inherited a large piece of land perfect for farming, if only she had someone to help her do the work. Wes makes her a proposition he hopes she can’t refuse. Accept his proposal of marriage, become a countess, and make both their lives better.
The problem? Penny takes one look at him and declares him the worst sort of rake. She’s right of course. But how far will he go to prove to her that he can change?