The Girl is Not For Christmas by Emma V. Leech

Miss Olivia Penrose is a lost cause and she knows it. She is just too stubborn to admit defeat.

After a series of disastrous investments, her family is on the brink of bankruptcy. Now, Olivia is the only thing standing between her brother Charlie’s rapidly growing family and penury. Olivia has one chance to capture the eye of a wealthy man and marry well. Her great aunt’s lavish New Year ball. Between now and then, Livvy must transform herself from who she is, into a woman who can drive a respectable fellow mad with desire. An impossible task.

I owe Ms Leech many happy hours of romantic escapism.

Ever practical, she knows there is only one man who can help with her transformation –
The notorious Earl of Kingston, dubbed the King of Sin by the scandal sheets, is recovering from the toll taken by his immoral lifestyle. With his own financial and private affairs in a mess, King escapes London to stay with his old friend Charlie for Christmas.

When his friend’s odd little sister demands his helps to learn the art of seduction, King is at once horrified, intrigued, and too bloody wicked to refuse.
Before the holiday is over, King is in way over his head, and must persuade Livvy that the King of Sin is dead, and he’s the man she needs.