The Venus and the Viscount by Scarlett Scott

A hellion. A hoyden. Scandalously flawed.
Flouting convention and shocking society has become the primary source of entertainment for Lady Charity Manners. She makes no apologies for her wild ways, nor does she have any intention of changing. As for marriage? No, thank you. She would far prefer to live an independent life on the Continent. Before she leaves England behind for good, she attends one last country house party for a reunion with her old finishing school chums.

A bore. A killjoy. Seriously staid.
When Neville Astley, Viscount Wilton, overhears Lady Charity describing him in unflattering terms to the lady he hoped to make his viscountess, he is outraged. How dare she attempt to meddle in his affairs and ruin his chances of gaining a bride? He is determined to deliver a stinging rebuttal and prove just how excellent a husband he would make.

Except, an odd thing happens when the man who has spent his life following all the rules confronts the lady who has gleefully ignored them. An attraction he never could have predicted sparks into flame. To his dismay, he discovers his inconvenient heart has chosen its allegiance to the most unsuitable lady at the house party.
But can Neville persuade Charity to pursue her dreams as his wife, or will he lose her forever?