A Wallflower Christmas by Lisa Kleypas
Though I have not read any of the other "wallflower" novels, I was caught by, yes, the pretty cover. :-)
The four "wallflowers" from the previous novels (I gather) are all settled and married in 1845 London, but when Rafe Bowman, a brother, arrives from America to meet Lady Natalie, they begin scheming a love match.
Unfortunately, Rafe falls head over heels in love with Hannah, Lady Natalie's companion, and a woman of a lesser class. We follows is a pas de deux between the two as they try to resist each other, eventually failing - miserably. ;-)
I really liked this novella (at just over 200 pages, a quick read), and I really liked the development between Rafe and Hannah, believing their attraction to each other, despite the rapidity of the novel.
A fun Christmas read - recommended!