E is for Edenbrooke by Julianne Donaldson.
Synopsis from Goodreads: Marianne Daventry will do anything to escape the boredom of Bath and the amorous attentions of an unwanted suitor. So when an invitation arrives from her twin sister, Cecily, to join her at a sprawling country estate, she jumps at the chance. Thinking she’ll be able to relax and enjoy her beloved English countryside while her sister snags the handsome heir of Edenbrooke, Marianne finds that even the best laid plans can go awry.
From a terrifying run-in with a highwayman to a seemingly harmless flirtation, Marianne finds herself embroiled in an unexpected adventure filled with enough romance and intrigue to keep her mind racing. Will she be able to rein in her traitorous heart, or will a mysterious stranger sweep her off her feet? Fate had something other than a relaxing summer in mind when it sent Marianne to Edenbrooke.
Confession: I haven't read this book yet. I bought it at a conference last year, had Julianne sign it (embarrassing note, I leaned in for a picture and totally put my hand on her thigh to keep balance and we really don't know each other and I didn't notice what I had done until I stood up and...yea...awkward). I just haven't quite got to it yet. But I have a feeling several others have read it - if you have, I'd love to know what you thought about it in the comments :)