The Lady and Her Duke by Ruth A. Casie

Could she use her skills as a lockpick to crack open the secrets to the murder as well as unlock his heart?
Lady Katherine Thornton has no interest in men after an indiscretion at her disastrous Season in London. No man can be trusted. Instead, she indulges in her fascination for gears and all things mechanical. Her unique drafting skill is an asset to her uncle Bennett Sutton, who is automating his textile factory. She doesn’t need anything else.
Lord Ian Wallace, the 4th Duke of Blackhall, is a retired military officer. An accidental duke after the deaths of his father and brother, he retreats from society and the clawing mothers and debutantes who stalk him. He’s focused all his energy on his partnership with Sutton. He’s satisfied and needs nothing else.
An oath to marry, a family legend to preserve, an uprising of the factory workers, and Sutton’s murder, throw Katherine and Wallace together to find a blackmailer and murderer.
They also will find two things neither knew they were missing…each other and their happily ever after.