At His Lady’s Command by Nicola Davidson

Welcome to the Surrey Sexual Freedom Society – where unconventional and uninhibited ladies and gentlemen discuss all matters erotic…
After twenty-five years in the British army, Captain Randall Denham thought he’d seen it all. Yet nothing prepared him for Lady Portia Butler, the fiercest, most exasperating, and amusing beauty he’d ever met—or how hard he would fall for her. Randall yearns to be at her command in the bedchamber as well as out, but a match between a highborn lady and a penniless ex-soldier of dubious birth is impossible.
Quite content to be unwed and childless, Portia cherishes her friends, her charitable causes, and outwitting the ton. She shouldn’t be having erotic fantasies about her bodyguard Denham…and definitely shouldn’t engage in a wicked secret affair with him. But when her family dictates she must cede her independence and marry a peer or face dire consequences, Portia faces her sternest battle yet: defeating the wealthy patriarchy to win the greatest prize of all—love.