Suzanne Enoch's "London's Perfect Scoundrel" - #2 in the Lessons in Love series
Lovely story, lovely characters. Saint is a complete jerk for at least the first half of the book, but as Evie gradually grows on him and reinstates his heart, he changes from the "perfect scoundrel" into a perfect hero. And thanks to Saint, Evie grows from a timid mouse into a brave woman willing to stand up for herself against fairly fearsome opposition.
I don't think Evie's brother gets his just deserts in the book, though - didn't see anything in the book to justify Evie's belief that he would make a fine servant of the people, and there is a great deal, especially his treatment of Evie, that indicates the opposite, but he comes out at the end of the story with an ascendant political career simply because of Evie's connection with Saint.
