Some of my problems with this story may be that it's the fourth in a series and it felt like it. Not having read the other stories, you know there's a lot of back-story you're missing, even though they aren't exactly required to follow the current story. 
 Woman decides the only way to support herself and her friends and family is to become a rich man's mistress. She's widowed and the gossips think she did in her husband. Her son-in-law threw her out of the house threatening police involvement, even though there's no proof she murdered her husband. When her plea for help to her brother comes to nothing, she makes her move, picking out a man she thinks she can seduce. 
 The man doesn't like to think she's doing the seducing. He thinks he's coming to the conclusion on his own. But when he finds out more about the woman, he decides he'd rather help her get back into society rather than use her. Of course, things get complicated and they end up engaged.