Never Spar with a Viscount by Lindsay Lovise

Ivy Bennett has escaped the marriage mart once already—by becoming a governess to the new Lord Brackley’s unruly little sisters. Spending her days in the schoolroom and her nights running a secret self-defense class for women, she has absolutely no interest in a husband. So when Ivy is handed a secret assignment by the spymaster known as the Dove, she sees an opportunity: fake a courtship with the enigmatic Owen Brackley to avoid her conniving father’s attempts to marry her off, complete the mission, and finally secure her freedom. Simple. Until it’s not.

Women across London are succumbing to a strange madness, and they all share a connection to Brackley—the same man who looks at Ivy like he sees right through her and is none too bothered by her lack of ladylike charm. As Ivy gathers gossip like breadcrumbs and dodges increasingly dangerous attempts on Brackley’s life, she realizes two things: someone wants the viscount gone, and the closer she gets to the truth, the harder it is to tell what’s real and what’s just part of the game.