An Offer From A Gentleman by Julia Quinn

This is the third of four books that I have read in this series, and it is pretty much a Cinderella story. Sophia "Sophie" Beckett, the illegitimate daughter of the late Richard Gunningworth, Earl of Penwood. He did not claim her as his own but he did bring her home as his ward, educated her. He provided for her in his estate, but his wife ignored his wishes so she is serving as a maid in the home of her step-mother, Araminta Gunningworth, Countess of Penwood, and two step-sisters, Rosamund and Posy Reiling. Sound familiar? In 1815, Sophie is 20 and assists her stepmother and stepsisters as they prepare for the Bridgerton family's masquerade ball. After they leave, the other servants help Sophie dress up to go to the ball, as long as she leaves by midnight. She dresses in a gown that belonged to her grandmother and she captures the imagination of the second Bridgerton son. He searched high and low for her, but comes up empty handed--because he isn't looking in any of the right places. He encounters Sophie years later and is again quite taken by her--only this time he does not see her as an option for marriage--this is a failing on his part of course, but this is a romance novel afterall. The step-mother gets her comeuppance and Sophie finds a way.