Highway Revenge by Nadine Millard

Evelyn Spencer has spent the last ten years living in her uncle’s house and longing for the day when she can leave and make her own way in the world. When she finds out her uncle’s terrible, hidden secret, Evelyn decides that she will first get revenge then leave and never set eyes on her wicked uncle again. Everything is going according to plan…until Viscount Andrew Ashdon comes along.
Andrew has been coerced into coming to spend a dull few weeks at his friend’s country estate. Used to intrigues, seductions and debauchery as a spy for the Crown, Andrew can think of nothing worse than rusticating in the country with no one around to entertain him…until he meets Evelyn Spencer. The race is on for Evelyn to get the proof she needs to prove her uncle’s deception and the last thing she needs is to be distracted by the devilishly handsome, rakish Lord Ashdon.
Can she achieve the impossible with Lord Ashdon’s help, by finally getting her revenge? And, more importantly, can she do it while keeping hold of her heart?