My So-Called Scoundrel by Fenna Edgewood

When one finds a bleeding, half-naked, indescribably handsome man in one’s bed, does one…
Scream
Faint
Hit him with a large book
Push him back out the window he climbed in
Bandage his wounds like a sensible bluestocking-in-the-making

The most perfectly imperfect debutante…
Marigold Spencer was never supposed to have a London Season. For heaven’s sake, she was never even supposed to become a lady! The former housemaid of a duke, Marigold is thrust into the limelight when her siblings marry far above their stations. Suddenly faced with the marriage mart, her escort and chaperone is not only one of ton’s most notorious scoundrels, but the utterly infuriating man still won’t tell her where he got the knife wound that led him to her bed that night.
…can still tempt the deadliest of rogues.
Lord Leigh Blakeley’s path took a sharp turn from seductive rake to vengeful assassin long ago. Yet when he finally returns home for a visit, he nearly ruins his new sister-in-law’s reputation for good by falling into her bed after a misadventure. Now Leigh finds himself forced to play chaperone to a debutante… one who unexpectedly enchants his cynical heart. And when Leigh foolishly proposes to teach the innocent young Miss Spencer something of the ways of pleasure, he ignites an inferno of passion that quickly turns unquenchable.
When another man presents Miss Spencer with an irresistible proposition, Leigh realizes the desire of his heart is quickly slipping away. Though he’s never intended to wed, Leigh finds himself making an offer Miss Spencer can’t possibly refuse… or can she?