The Viscount Who Loved Me by Julia Quinn

But this time the gossip columnists have it wrong. Anthony Bridgerton hasn't just decided to marry--he's even chosen a wife! The only obstacle is his intended's older sister, Kate Sheffield--the most meddlesome woman ever to grace a London ballroom. The spirited schemer is driving Anthony mad with her determination to stop the betrothal, but when he closes his eyes at night, Kate's the woman haunting his increasingly erotic dreams... Contrary to popular belief, Kate is…