The Lady is Daring by Megan Frampton

Five well-bred sisters, one sensational scandal. Now the Duke of Marymount’s daughter Ida is about to find love in the most unconventional way…

It was easy for society to overlook Lady Ida Howlett; they found her bookish, opinionated, and off the marriage mart. But little did they know that behind a calm exterior beats the heart of an adventuress, one who, determined to discover her runaway sister’s whereabouts, steals a carriage and sets off on a daring mission. Then she discovers she’s not alone! Bennett, Lord Carson, is inside, and he refuses to leave.

Lord Carson’s plans had always been to find a soft, gentle wife who would run his home and raise his children. Still, he makes a bargain with Ida—he won’t desert her during her mad adventure. He’ll make sure she’s safe, and then find a suitable lady to fall in love with. But when rules (and garments) become discarded during this long, intimate journey, it’s soon clear that this surprisingly daring lady is the woman he’s needed all along.