A Most Unsuitable Man

A Most Unsuitable Man was first published on 1st Feb 2005 by Signet [0451214234].
It became available as an e-book, 1st Aug 2006.
An audio edition was published by Recorded Books in 2005 on CD [1419346059]; cassette [1419346032]; and for download [9781440759284].

Read an excerpt of this book here.

Damaris Myddleton is very rich, but she doesn't belong in the glittering word of the aristocracy. She hopes to change that by marrying the Marquess of Ashart, and when he chooses another, her world falls apart. She is prevented from running away by Ashart's penniless friend, Fitzroger, who also helps her regain her foothold among the elite. Now she can plan another grand marriage, this time to a duke. Something about Fitzroger makes her uncertain of her plans, but he really is a most unsuitable man...

I think this Gainsborough portrait from the right period looks a little like Damaris.

"A little tall, slim, straight-backed, apparently confident.
  Brown hair, commonplace features, bright eyes, wide smile. Long lidded eyes, cat like."