A Governess of Prodigious Skill by Emily E K Murdoch

When a governess of prodigious skill is required, there is only one place the nobility of England go: the Governess Bureau.
Miss Helena Patrick is not a governess. At least, not really. The famed and celebrated actress is a little down on her luck, and grasps the chance to masquerade as a governess until better luck comes around. Worse luck for her, she’s stuck out in the country with a master who is afraid to leave his house with a wife who died but no one will speak of, his sister who mysteriously disappears whenever anyone wants her, and a brother who…A brother who absolutely should not be kissing her. Especially as he’s a duke.
Oscar Fernsby, Duke of Kilerth, only planned to visit his brother for a few weeks. Prove the man was fine, then return to London to continue his anonymous bare knuckle boxing fights. Until a woman he thinks he recognizes but cannot place turns up at his brother’s house, blackmails him into silence, and distracts him with her beauty and strange skills.
Because this Helena, the governess, is strange. More at home with a sword in her hand than chalk, Oscar knows that something isn’t quite right. The only way to discover her secrets is to get close to her. What a shame.
Everyone at the Old Abbey has secrets, but it will take a governess of prodigious skill to discover them all – and keep her own a secret…