After knocking her BIL into a pond at a party when she discovers him with another woman, Lady Sophie Talbot (who hates her title and the ton) decides she’s had enough and flees. 

Unfortunately her escape lands her in (on) a carriage she thought was headed to Mayfair but is decidedly not. 

The carriage belongs to Aloysius Archibald Barnaby Kingscote “King,” Marquess of Eversley, Future Duke of Lyne (LOL), a first rate rogue and ruiner of ladies (for reasons). 

Mutually suspicious and antagonistic, Sophie and King, after a series of curricle races, meddling friends (new and old), highwaymen, gunshot wounds (yup), and false professions of marriage end up on a road trip to her childhood home and his family seat. 

As their journey progresses their feelings change. Their relationship becomes physical. Mistakes, tons (mostly his), are made. Families get (unhelpfully) involved. Secrets are exposed. Love is expressed. Hearts are broken. A wedding happens. She leaves him. He realizes his errors. Forgiveness is begged and eventually given. And he buys her a bookshop. 

I love MacLean.