Dreaming of You by Lisa Kleypas (1994, Paperback, Reissue)

In the shelter of her country cottage, Sara Feilding puts pen to paper to create dreams. But curiosity has enticed the prim, well-bred gentlewoman out of her safe haven--and into Derek Craven's dangerous world.

A handsome, tough and tenacious Cockney, he rose from, poverty to become lord of London's most exclusive gambling house--a struggle that has left Derek Craven fabulously wealthy, but hardened and suspicious. And now duty demands he allow Sara Fielding into his world--with her impeccable manners and her infuriating innocence. But here, in a perilous shadow-realm of ever-shifting fortunes, even a proper "mouse" can be transformed into a breathtaking enchantress--and a world-weary gambler can be shaken to his cynical core by the power of passion. . .and the promise of love.