The Perfect Duke

Nicholas Lidgate, the Duke of Ravenshire, needs to marry a lady who comes from a wealthy family. His father left a large sum of debt, and if he doesn't pay it off, he'll be sent to debtor's prison. He has two very important advantages. One, he is a prominent member of the Ton. Two, no one knows his secret. If he can secure a marriage to a lady from a wealthy family, all of his problems will be over.
He proposes to Miss Tara Webb because her dowry will be enough to pay the debts and leave him with a comfortable lifestyle. He doesn't mind the fact that she only agrees to the marriage because her connection to him will bring her social group back in good standing. A marriage of convenience suits him just fine. What he does mind, however, is the fact that her brother turns out to be one of his father's debtors, and her brother isn't one to play fair. Also, the more Nicholas gets to know Tara, the more he ends up falling in love with her.
And her brother will use that to his advantage.