Marcus is a Duke and a widower. On her deathbed, his slightly evil mother tells him that she promised an old friend that he would marry the friend's ward. Needless to say he is not thrilled about this prospect. He has enough to deal w/ looking after/rebuilding his crumbling estate and dealing with his scapegrace younger brother.
Lady Miranda Grey is the daughter of a peer......but a peer who has gambled away the family fortune. Miranda's father isn't totally a baddie. He got the wake up call and did hard manual labor to try and keep the family together and keep Miranda from winding up on the street selling herself or being a man's mistress. She goes to visit the Duke with low expectations but he does the right thing and marries her.
I was worried at first, having read these kinds of stories before, that the no good evil brother would completely muck things up beyond salvaging. Luckily things didn't go as bad as I feared, but I was very relieved when Marcus & Miranda finally came clean with each other.