A Wager Worth Winning by Nadine Millard

Annabeth Langton has come from the Americas with big shoes to fill. Both her sisters had managed to take London by storm and marry two of the most eligible peers in Christendom. Well used to being in her sisters’ shadows, she still can’t help wishing for a grand adventure of her own. But with the eyes of the notorious Monster of Montvale Hall watching her every move, she knows her chances of romance are laughably small.
William Sandon, Earl of Tenshire has never met a bet he wouldn’t try to win, never met a challenge he didn’t want to take. So when his friend bets that he won’t get near the ton’s most cosseted debutante, he can’t resist placing the wager of a lifetime. Miss Annabeth Langton might just be the most protected woman in England. But that just made the wager even more worth winning.
A house party in the countryside affords Will the chance to put his plan into action. But the best laid plans can sometimes go awry and the longer he spends in the company of the beautiful Beth, the more he wonders if she might just be more than a wager worth winning.