My Lord Hercules: Regency Seasons, Book 3 (Unabridged‪)‬

Miss Miranda Bartlett is on a mission to locate her missing friend. Determined hoyden that she is, she'll do whatever it takes to get the answers she seeks, too, even if that means dressing like a dandy, sneaking into a gaming hell, and surrounding herself with London's worst reprobates. However, she didn't plan on bumping into a Herculean gentleman along the way. The handsome and honorable Lord Harrison Casemore immediately thwarts her plans and seems determined to save her at every turn, making it more than difficult to accomplish her task.

Ever since Harry Casemore spotted the exotic temptress trying to pass herself off as a fop, he's been drawn to her. He hasn't figured out what she's after, but he's fairly certain he'd sell his soul if she'd just let him help her with whatever it is.