A Fugitive Green — Diana Gabaldon

The #1 New York Times bestselling author of the acclaimed Outlander series weaves a captivating story of secrets and intrigue, bringing together Lord John's elder brother, Harold Grey, and his future wife, Minnie. This novella, originally published in Seven Stones to Stand or Fall, is now available as a standalone ebook.
 
Minnie Rennie and her father operate a family business dealing in rare books and letters -- with a sideline in forgery, blackmail, and burglary. After traveling from Paris to London for work, with a secret mission to find the mother she never knew, Minnie's clandestine meeting with a client pseudonymously named Mr. Bloomer is interrupted when she crosses paths by chance with Harold Grey, Earl of Melton (and the Duke of Pardloe, though he spurns the title).
 
An outcast from society, Hal is beset by troubles. Not only is he grieving the deaths of his wife, Esmé, and their unborn child, he's still in shock over the revelations of her infidelity -- an episode that ended with Hal killing her lover, Nathaniel Twelvetrees, in a duel. Minnie and Hal are immediately drawn to one another, but when Mr. Bloomer asks her to steal potentially incriminating letters between Esmé and Nathaniel that Hal still has in his possession, she finds herself swayed by fascination and empathy for a man she barely knows.